Which layers are being displayed in the Gerber viewer? And, how are they ordered in the viewer, from top to bottom?
It looks like the colors from many layers are mixing together and obscuring information from the layers. Try displaying only one or two layers at a time, adjust the color assignments, and play with the display ordering of the layers. You may also have some control over the “transparency” of each layer’s color.
I can’t help you with specific details because I use the “gerbv” viewer, from the gEDA project, instead of KiCAD’s “GerbView”. And with that Gerber viewer I seldom display more than 2 or 3 layers at a time. I’m usually looking for specific problem areas that pertain to particular layer pairs - e.g., silkscreen overlaying bare copper; insufficient solder mask clearance; etc - so I display only the layers involved with the potential defects.
If you can’t get the results you’re looking for, can you post your Gerber file set? Somebody may know how to set up the viewer to get the display you’re looking for.