Mold growth due to high humidity? Perhaps staining from a but of rust from the material the filter is built with?
I’ve never seen anything like that.
I would carefully pull that out and clean the pre filter. Then either use the sun to bleach it and the entire filter, or use hydrogen peroxide and water mix to spray it. There’s other sprays that will work too
How bout a normal picture … Can’t nobody tell you anything for sure with a giant purple color picture!!!