In my experiment, I had white colonies initially and they turned yellow. So I thought it´s natural that mature E. coli colonies are yellow and young are white. But it could be that I had two types of E. coli and the yellow one just dominated the white.
I research the affect of vitamin C on susceptibility of E. coli to H2O2. First I treat bacteria with vitamin C, incubate for an hour and H2O2.