I found some example today, same terrain- 2 different shades of blue (at least in overlapping areas, on this screen bacterias don't exist on some small patches of terrain)
View attachment 379393
There's often a height differential on different bios, maybe due to atmospheric pressure or other effects, so the blue layer will reflect height differently depending on where it's targeted for that bio. As you can see on the right the bare patches look like higher ground, so the bio environment is targeted maybe towards depressions where the atmospheric pressure is higher, the one on the left however appears the same all the way across.
The blue layer is an clearly an overlay that probably doesn't hug the surface, we can't really tell that because we can't see it once we come out of glide, but it is an overlay, so not just coloured ground. The blue area on the left may be projected higher above the surface than the one on the right, where the bare ground patches show because the left bio can exist in all the different terrain height or atmospheric pressures represented here. Because there's a much larger gap between the overlay and the ground the ground on the left the terrain doesn't show through as much. Keep in mind this is speculation, the only people who know how it really works are FDEV, but it's a possibility than can explain why the blue is different colours for different bio, because of the height of the overlay from the underlying terrain.
You can just see on the left light blue patches that represent the bare ground on the right, so I would say the overlay on the left is much higher to catch the higher terrain and therefore harder to see the underlying terrain, where on the right you can clearly see the craters which are all but invisible on the left because the overlay is much closer to them.