moved to the VFT forum. If I recall there was another question on red coloring recently.
The more sun the plant gets the more red in the trap. Although some varieties will stay green or at most get a pink blush. Slowly acclimate your plant to brighter light so you don't give it sunburn.
For some reason my traps got red within a week of me putting them outside. I give them southern exposure and they are doing excellent! Today it was 105 degrees here in Illinois, I just give them plenty of water and they do really good.