Question

Why do light-fur mice survive LESS often on dark rocks, compared to dark-fur mice?

Answer 1

Answer:

for a creature with a lighter fur color it is next to impossible to blend into darker colored environments compared to darker fur colored creatures

Answer 2

Answer:

Light-fur mice survive less often on dark rocks because they are easily seen by predators while dark-fur mice are harder to see.

The same situation applies to dark-fur mice on light rocks.