I know someone who did a winning school science fair project by growing plants under different colors of cellophane. Her big brother suggested the project. My daughter sort of tried it, but she didn't really finish the project.

I have some succulent plants that have purple-black leaves when the sun is bright, but the leaves gradually get greener when there's less sun and the nights are longer.

This website says blue light helps leaves grow, and red + blue light helps plants flower:
click here please

This website tells about what each color of light does for plants:
please click here

Plants will grow poorly if they don't get the color of light that their chlorophyll molecules need for energy.

Here's a ScienceLine answer about this:
scienceline answer

Some flowers, like hydrangea, are blue or pink or lavender, depending on how much acid is in the flowers. You can see this change in color with blueberries if you crush them up and add vinegar to some of them and baking soda to others. Vinegar is an acid, and baking soda is not an acid; it's a base.

Thanks for your question, Sadie - I enjoyed answering it!