Hello, I am wanting to make it so that when I press the tab key, all instances of an object with the tag "enemy" get a glow.
The problem here is not the toggling, but the glow itself. A halo is too small, and I want it to look better than that anyways. So, my question being, how do I make an object glow, without it being affected by post-processing effects (aka, greyscale), and to make the glow fit around the object? Is this even possible?
If you have Unity Pro, you can use the Glow effect. You can control it so that only the desired objects glow by changing the alpha value of the material's tint colour (you can do this in code via Material.SetColor). The glow shader uses the alpha value output by materials to determine the glow amount, so set the alpha to zero on all materials except the ones you want to glow.
The ordering of the post-processing effects on your camera determines which effects are affected by which other effects. They are performed in the order that you added them to the camera, so add the glow effect last, if you wish it to be applied after all other post processing effects.
There are other methods of making objects glow such as just increasing the RGB values of their material's tint colour, or creating a larger mesh which surrounds or covers your object, and giving that a material with an additive shader. If you're just looking for any kind of special effect to highlight an object, you could even use a particle effect at the same position as the object to give it a twinkling sparkly look :)
M50, it sounds like you want an "aura" type effect with the model still the same color but a red/blue glow around the model indicating the werewolf special vision. For that effect I'd echo Duck's suggestion of a secondary model scaled up slightly with a semi-transparent material or adding a mesh particle emitter to your models. If you can make it work with a post-processing effect that will probably minimize the amount of logic you need in each character that needs to have the glow, but then you need Pro.