Transparent gameobject with textures

Hey guys,

I am really tired of searching about this problem so I will ask here. I am making a new building system. When someone wants to build he clicks the button with certain tower and tower is set to cursor. I want to make that tower colored by red color if he cant build where is he pointing to and if he can build I want to make the tower transparent. Something like this https://www.assetstore.unity3d.com/en/#!/content/7793

Does anybody know some tips or tricks how to do it please?

Best regards,
MonK.

See:

The example on this page animates the colour of the object between green and red.