I doubt it. Sounds like the peat is staining the perlite. Very common and nothing to worry about.

I just found out, i asked one of the guys at cobraplants (sarracenia northwest) and he said it is fungus and it kills plant seedlings quickly( within 2 days) but it doesnt effect adults. I have one seedling but i dont hace any fungicide with me

If the yellowing is just a stain, it is no problem.. but you indicated that it was just replanted, so the perlite should be new. Yellow fungus will grow up as a soft lump and get bigger as it responds to water trying to spread to any organic matter it can.

I agree with the two follow ups. Have you ever seen the color that peat moss turns water? The perlite's capillary and evaporative action tends to trap some of that colorant (tannin?).

I too have yellowing perlite in my seedling dish that gets regularly sprayed with fungicide (and the yellowness remains). So unless its furry or squishy, its probably just staining and nothing to worry about.

Probably wouldn't hurt to get some fungicide and spray it anyway though.