I believe that one wall is basically a blue colored wall or part of it. Maybe the cat is caught up with blue field entoptic phenomenon and of course a cats eyes can take in far more light than a human specially at night so the cat would not need a super bright blue background in order to see the movement in the capillaries.

while we are at it how about ....... https://www.petplace.com/article/cats/pet-hea...y-for-cats