Bacteria growth on Simmon Citrate Agar

[Venchea]

I need to transfer plasmids from Escherichia coli into Cupriavidus necator. I've done the transconjugant transformation of plasmid from E. coli to C. necator on LB plates without antibiotics. To isolate out the transconjugants, I transfer the bacteria colonies from LB plates to Simmon Citrate Agar plates which will select out the C.necator conjugants since E. coli can't utilise citrate as carbon source and the Simmon Citrate Agar were supplemented with kanamycin to inhibit the growth of C. necator without plamsid in it. The plates were incubated at 30oC which serves as the optimum growing temperature for C. necator. The problem I am facing now is there are colonies on Simmon Citrate plates but then the agar remain green in colour which it's supposed to be blue after the bacteria utilised the citrate and change the medium into alkaline pH. So, I'm wondering are the bacteria colonies on Simmon Citrate Agar are C. necator with plasmids or E. coli with plasmids?
Can anyone tell me the answer???? Thanks a million.