I have also heard that starving the flytrap will cause the traps to turn red, but I don't know if it is true or not. I grow my flytraps on my porch rail. They get sun from about 7:30 to 3:30 and have nice red traps.
It's possible that you have a variety that stays green.
The first is a typical.The second and third is a big mouth.I know were to get them.www.************ has them in November.I would like to know if I could make some of my fully formed traps of the common flytrap turn red?Or does the red only appear on new growing traps if in full sun?