I have been banging my head against the wall with this one…
I can’t find the location of the syntax highlighting color templates on a MAC installation of MonoDevelop (the version which comes with Unity, NOT the standalone version).
The problem is that I was making my own syntax color template and installing it through the preferences/syntax highlighting option panel in Mono, but I made a type error at one point and now I get an error everytime I access that option screen, and I can’t even change to a different template anymore because nothing shows up now.
I need to manually remove my custom templateStyle.xml file from the folder where it installs these, but I cannot for the life of me find that folder. I even tried uninstalling Unity and re-installing it (after getting rid of all the Unity/Mono local folders in Library), but I still get the same error when accessing the syntax highlighting properties pane 
Does anyone know the location of the syntax highlighting templates on a MAC OS X install of Unity/MonoDevelop?
I finally figured out, after many hours of banging my head against the wall…
So, in case anyone ever runs into the same problem, here’s the solution:
First you have to turn on “Show hidden files”, then you can access the following folder:
/Users/$username/.config/MonoDevelop-Unity/syntaxmodes
This is where MonoDevelop copies custom syntax highlighting color templates when you add a new one through the preference/syntax highlighting pane.
So if you ever install a corrupted theme by mistake like I did, you’ll know where to find it to delete it, and you won’t have to uninstall and re-install Unity a dozen times 
sorry to intrude, but can you tell me how to make custom syntax color schemes for monodevelop? I can’t find it in preferences or any of the other menus in Monodevelop.
You can add custom template in “Preferences > Text Editor > Syntax Highlighting”
There you will see a box with all the currently installed templates, where you can choose which one you wanna use, remove them, or add new ones with the “Add” button. The template file has to be an “XML” file (yourfile.xml).
What I have been doing is creating my own template and putting the file in a local directory on my computer, which one doesn’t matter. Then just click the “Add” button and you will be able to browse for your custom template file. So browse to the location where you saved it and select it. If it imports successfully (assuming you file syntax is correct), you will then be able to select your new template and use it.
Then when you make changes to your template (in your local template file), you need to first “Remove” your custom template from the list using the “Remove” button, then re-add it and re-select it (kind of a pain but it’s the quickest way I found to make quick changes).
Here’s a link to a quick “how-to” which really helped me:
http://www.teknynja.com/2009/10/monodevelop-custom-color-schemes.html
And here’s a sample (the template I’m currently using), save it as an .xml file:
<!-- SRStyle.xml
Author:
Stephane Roncada
-->
<EditorStyle name="SRLight" _description="Light color scheme using blue, green and red colors.">
<!-- ubuntu palette -->
<Color name="orange_highlight" value="#eec73e"/>
<Color name="orange" value="#f0a513"/>
<Color name="orange_base" value="#ff6600"/>
<Color name="orange_shadow" value="#f44800"/>
<Color name="environmental_blue_highlight" value="#aaccee"/>
<Color name="environmental_blue_medium" value="#6699cc"/>
<Color name="environmental_blue_base" value="#336699"/>
<Color name="environmental_blue_shadow" value="#003366"/>
<Color name="accent_yellow_highlight" value="#fdff99"/>
<Color name="yellow" value="#ffff00"/>
<Color name="accent_yellow_base" value="#fdca01"/>
<Color name="accent_yellow_shadow" value="#986601"/>
<Color name="accent_blue_highlight" value="#b3defd"/>
<Color name="accent_blue" value="#0197fd"/>
<Color name="accent_blue_base" value="#0169c9"/>
<Color name="accent_blue_shadow" value="#013397"/>
<Color name="accent_orange" value="#f44800"/>
<Color name="accent_red" value="#fd3301"/>
<Color name="accent_red_base" value="#d40000"/>
<Color name="accent_deep_red" value="#980101"/>
<Color name="accent_green_highlight" value="#ccff99"/>
<Color name="accent_green" value="#98fc66"/>
<Color name="accent_green_base" value="#339900"/>
<Color name="accent_green_shadow" value="#015a01"/>
<Color name="human_highlight" value="#fdd99b"/>
<Color name="human" value="#d9bb7a"/>
<Color name="human_base" value="#816647"/>
<Color name="environmental_shadow" value="#565248"/>
<Color name="ubuntu_toner" value="#002b3d"/>
<Color name="accent_magenta_highlight" value="#ff9bff"/>
<Color name="accent_magenta" value="#ff00ff"/>
<Color name="accent_dark_violet" value="#6600cc"/>
<!-- custom colors -->
<Color name="main_bg" value="#e9e9e9"/>
<Color name="linenumbers_bg" value="#dbdcdc"/>
<Color name="iconbar_bg" value="#e4e6e7"/>
<Color name="iconbar_separator" value="#bdbebf"/>
<Color name="marker_line" value="#e7e5e5"/>
<Color name="marker_line_changed" value="#cfcdcd"/>
<Color name="comments_green" value="#4b820a"/>
<Color name="string_darkred" value="#a82000"/>
<Color name="text_lightgrey" value="#999999"/>
<Color name="text_grey" value="#454545"/>
<Color name="text_darkgrey" value="#333333"/>
<Color name="text_lightblue" value="#0087dd"/>
<Color name="text_mediumblue" value="#0c6bd6"/>
<Color name="text_darkblue" value="#00508e"/>
<Color name="text_darkgreen" value="#1f7401"/>
<Color name="text_violet" value="#da00e8"/>
<Color name="text_purple" value="#7d21e5"/>
<!-- environment -->
<Style name="text" color="text_grey" bgColor="main_bg"/>
<Style name="text.selection" color="human_highlight" bgColor="text_darkgrey"/>
<Style name="text.selection.inactive" color="human_highlight" bgColor="darkgray"/>
<Style name="text.background.searchresult" color="yellow"/>
<Style name="text.link" color="blue"/>
<Style name="caret" color="black" bgColor="linenumbers_bg"/>
<Style name="marker.line" color="marker_line"/>
<Style name="marker.line.changed" color="marker_line_changed"/>
<Style name="marker.line.dirty" color="marker_line"/>
<Style name="marker.ruler" color="accent_blue_highlight"/>
<Style name="marker.whitespace" color="human"/>
<Style name="marker.invalidline" color="accent_red_base"/>
<Style name="marker.bracket" color="environmental_blue_medium" bgColor="environmental_blue_highlight"/>
<Style name="marker.bookmark.color1" color="human_highlight"/>
<Style name="marker.bookmark.color2" color="human_base"/>
<Style name="marker.template.primary_template" color="accent_green_shadow" bgColor="accent_green"/>
<Style name="marker.template.primary_highlighted_template" color="accent_green_shadow" bgColor="accent_green_highlight"/>
<Style name="marker.template.secondary_template" color="white" bgColor="white"/>
<Style name="marker.template.secondary_highlighted_template" color="human" bgColor="human_highlight"/>
<Style name="linenumber" color="text_darkgrey" bgColor="linenumbers_bg"/>
<Style name="linenumber.highlight" color="accent_red"/>
<Style name="iconbar" color="iconbar_bg"/>
<Style name="iconbar.separator" color="iconbar_separator"/>
<Style name="fold" color="text_lightgrey" bgColor="linenumbers_bg"/>
<Style name="fold.highlight" color="accent_red"/>
<Style name="fold.togglemarker" color="text_darkgrey"/>
<!-- highlighting -->
<Style name="comment" color="comments_green"/>
<Style name="comment.tag" color="comments_green"/>
<Style name="comment.line" color="comments_green"/>
<Style name="comment.tag.line" color="comments_green"/>
<Style name="comment.block" color="comments_green"/>
<Style name="comment.tag.block" color="comments_green"/>
<Style name="comment.doc" color="comments_green"/>
<Style name="comment.tag.doc" color="comments_green"/>
<Style name="comment.keyword" color="comments_green" weight="bold"/>
<Style name="comment.keyword.todo" color="comments_green" weight="italic"/>
<Style name="text.literal" color="accent_magenta"/>
<Style name="text.punctuation" color="accent_magenta"/>
<Style name="text.preprocessor" color="text_purple" weight="italic"/>
<Style name="text.preprocessor.keyword" color="text_purple" weight="bold"/>
<Style name="text.markup" color="accent_blue_base"/>
<Style name="text.markup.tag" color="accent_blue_shadow"/>
<Style name="constant" color="accent_red"/>
<Style name="constant.digit" color="accent_red"/>
<Style name="constant.language" color="accent_red"/>
<Style name="constant.language.void" color="text_lightblue" weight="bold"/>
<Style name="string" color="string_darkred"/>
<Style name="string.single" color="string_darkred"/>
<Style name="string.double" color="string_darkred"/>
<Style name="string.other" color="string_darkred"/>
<Style name="keyword" color="accent_red_base" weight="bold" />
<Style name="keyword.access" color="accent_red_base" weight="bold" />
<Style name="keyword.namespace" color="text_darkblue" weight="bold"/>
<Style name="keyword.property" color="text_lightblue" weight="bold"/>
<Style name="keyword.modifier" color="text_darkblue" weight="bold"/>
<Style name="keyword.type" color="text_lightblue" weight="bold"/>
<Style name="keyword.declaration" color="text_darkblue" weight="bold"/>
<Style name="keyword.access" color="black" weight="bold" />
<Style name="keyword.operator" color="text_lightblue"/>
<Style name="keyword.operator.declaration" color="text_darkblue" weight="bold"/>
<Style name="keyword.selection" color="text_darkblue" weight="bold"/>
<Style name="keyword.iteration" color="text_darkblue" weight="bold"/>
<Style name="keyword.jump" color="text_darkblue" weight="bold"/>
<Style name="keyword.context" color="text_darkblue" />
<Style name="keyword.exceptions" color="text_darkblue" weight="bold"/>
<Style name="keyword.parameter" color="text_darkblue" weight="bold"/>
<Style name="keyword.misc" color="text_darkblue"/>
</EditorStyle>
WOW ronronmax. You’re doing it tough. For such a “heavy” program, it’s amazing monodevelop doesn’t have some syntax and theme editing facilities built in. TRULY amazing. The thing is enormous. Well over 200 MB. And Soooo slow on a mac that I can’t get into using it.
Tried your template. It’s very subdued. Nice!
You got any ideas how I can make UnityScript keywords come out in a distinctive color on MonoDevelop? For me, some of them are, like “configurableJoint” is, but not things like AddForce etc…
And another thing that pisses me off… it seems to know what my variables and functions are, but how do I color them differently so I can see them clearly in code?