Colour change

[hornydevil]

Got a couple of red rosetted typical VFTs last month and have since repotted them to bigger pots. New shoots, leaves and traps sprouting huge and beautifully but noticed that the traps do not have the same colour as the older traps that came with the plants.
Have read in previous threads that it takes a change of day and night temperature of minimum 6 - 10 degrees for the colour to be maintained.

My question is, how do I get get this done; the difference in temperature; short of taking them indoors for a/c at night. Staying in the city and with the present haze conditions, a drop of 2 degrees is already a God send!