Are the images deliberately overexposed (in which case what's the point of RGB sets?) or is this just due to histogram stretch acting up again?
Here's a shot of Jupiter taken almost three years ago. Two blue-filtered NAC images stacked and enlarged 5x:
The GRS is not detectable in the image because it probably wasn't visible at the time, Solar System Simulator doesn't produce valid GRS locations for Jupiter. Probably the texture map is synched to Jupiter's mean rotation, not the spot's rotation.