Issue is caused by scaling for power of 2 dimensions and mipmapping that happens through GLU. It looks like the library cannot handle float colour values above 1.0 correctly. Since we are close to release I will just clamp the srgb result for now even though it will result in a small performance loss for 16 bit textures only. I tried a few things before that, glGenerateMipmaps + no scaling (supported for 2.0 GL hardware and up), or using our own scaling instead of glu among them which worked very nicely and gave a speedup too. However, since we are close to release and there may be issues with GPU mipmap generation, see: http://www.gamedev.net/topic/495747-another-glgeneratemipmap-question/ (old discussion but better be sure than sorry) I went for the most compatible solution. Maybe after release this can be tested if other devs agree.