What's the difference between : Multiply, Add, etc In some of nodes input, the RGB Mix for example, there are several settings : "Multiply", "Add", "Mix", etc... what is the difference between them?
This is a different color blend modes like in 2D drawing programs like Gimp, Inkscape, Photoshop, Imagemagick, ets

For example, if you chose add, colors from first input will be add to second witch makes bright sum of both inputs.  



Here is detailed explanation about blend modes in gimp manual