How do I change the color of a texture in a specific radius?

I am working on an idea where I have several colored characters moving around a white map, and as they move I want them to leave a trail of color behind them, however I cannot find anything about changing color of textures in real time.

I have though of other ways to achieve this effect, like placing a model with a proper colored texture on top of the surface.

A while back in XNA I used render targets to create a black overlay for a map and cleared a circular area around lights using alpha blending.

If any of these things are possible, any advice on how to proceed would be greatly appreciated.

Thank You.

actually I have done a lot of this! And nice name!

Every time that you use another texture it uses a lot of processing power.

You’re supposed to use one texture with lots of colours like a pallette, and use it like a texture Atlas. get whatever meshes you want texture, when you instantiate them, and change all their UV coordinates to a single point, for example if you wanted them to be white, change all the UVs to 1, 1, the corner of the pallet, and 0.5, 0.5 let’s say would the blue.

You would need an image you know the colour coordinates of, but that’s a very efficient way to do it in unity, there is even a code somewhere on this forum by someone Bentley I think to change mesh UVs into points.-that’s the way I would do it because it’s really convenient to know how to do, I should upload it to unify wiki actually. How to move UV's of a mesh so you can have two textures in one file - Questions & Answers - Unity Discussions

Another option is that you can change the colour in code of the material
http://wiki.unity3d.com/index.php?title=Animated_Color_Procedural_Texture

Although I think that uses the same as a different texture for every texture, maybe it’s okay if you use shared material, I don’t think it’s draw call efficient.

another thing to know about is there is a shader that allows you to use to textures with transparency on an object in the unity wiki.