How did the sunlight affect the flower grow?

The leaves and stems of a sunflower are green -- they are reflecting, not absorbing, green light. The colors that give the plant the most energy are at the purple end of the spectrum (red and blue) - those colors with the highest light energy.

Blue light - responsible for vegetative or leaf growth (fluorescent light)

Red plus Blue light - encourages flowering (full spectrum or "grow lights)
dark colors, not light