Sunlight to a VFT is extremely important for its best growth. However, the sun, though responsible for the coloring process, is not the whole picture. We all know that anthocyanin cells in CP is the cause of their coloration. How a VFT colors up, and the "triggers" involved are another story. The old assumption of, "put the plant in the sun to promote the red coloration" is wrong. Yes, the plants may have genetics that respond to full sun, and the plants redden up. However, their are other triggers that have nothing to do with full sun that will turn the plant into a kaliedoscope of color. How the sun shines on some VFT's is the "secret" to their coloration. Some color up only in bright shade. Some will only respond to sun filtered through tall grasses or the dappling effect it would get through the branches of a tree. Many variables will produce bright, rich color, while some, genetically, won't color up to any extent, no matter what you do. So light is the key, but the most important factor, is how the sun shines, or doesn't shine, on a particular plant. The fun part is experimenting with your baby until you get the coloration you are looking for, using the guidelines above. Expect to to get negligable results from some of your babies too! In the CP world, nothing is usually an absolute in the life of a CP/VFT! EXPERIMENT!!! I did.
Remember, sun is only a small part of the result. Kick it around a while. See what works for the coloring up of your VFT's.