this is a real challenge. After electroplating I would grow up the conolies for a few days and then perform colony per on 10 or 20 colonies to id those that have the reporter using specific primers for the reporter and then subclone positives and grow up clones under very high selection. Use non transfected bugs to establish concentration of lethal antibiotic dose a priori.

thanks lora. So my transformed colonies should look red or pink as the reporter plasmid expresses mCherry . But my colonies are still white.

It may depend to some extent on which resistance marker you are using, for many or even most I don't think you are going to be successful. Once you get high level resistance then adding more copies of the resistance gene is not going to contribute much. The simplest thing is to use a plasmid with a different resistance marker.