Fix for Visual Studio color and bgcolor unresolved symbols

[HDuft]

I've been having an issue with compiling with Visual Studio rather than Cmake (funnily enough I'm porting my project to Cmake soon) and I've noticed a few others have the same issue with color and bgcolor unresolved symbols.

I found renaming one of the color.cpp files to color2.cpp fixed the issue so I think VS doesn't like the name collision.

Just thought i'd note it for anyone with the same issue and if you want to make the project buildable from source in VS.

[ArthurSonzogni]

Hello! Thanks for reporting this!

How does it work in Visual Studio? I was expecting Visual Studio to "understand" cmake and use it under the hood when provided. At least, this is what I do when I do test on Windows from time to time.

Searching online, the issue your are reporting seems real:

• https://stackoverflow.com/questions/9351132/two-files-of-the-same-name-give-linker-error-in-visual-studio
• Visual Studio object file collision detection needs tweaking premake/premake-core#1187

I am happy to merge a PR renaming color.cpp to color_.cpp if this helps to overcome Visual Studio problems.