Sorry for being pendantic, but as stated, tga doesn't have a palette..

The reason for the problem is that the images saved with photoshop are in the RGB color space, while (apparently, according to Phemox) GIMP natively uses CMYK. Converting from one color space to another is done with a formula. I believe that converting from RGB to CMYK never results in a perfect match, but it might also just be a problem of the GIMP.

Whatever be the case, this is a problem of the GIMP, since all mainstream file formats store RGB, and so does TGA (RGBA actually). Engines (including Gamestudio) work with RGB, the output of pixel shaders is RGB, etc..

Here is an interesting link: Color spaces