Agar plate discoloration

Hello! I am currently a student doing a research paper about using weak organic acids as preservatives and microbial growth inhibition so I did an experiment. However, I got a small problem where there was no growth on the plates and instead a weird discoloration as showed in the picture. I don’t know if this is some sort of microorganism or if it the acids that caused the discoloration.

I was wondering how I should write about it in the discussion and what the cause is. Thank you in advance.