In the National Gallery of Art Sculpture Garden grows a brilliantly-colored plant which I later determined is coleus.
It made me remember an article I read in 2015 which claimed that plants should be purple, because green light carries the most energy (and green plants reflect green light).
It's a great evolutionary game theory story, but I wasn't able to verify the details. I couldn't even find a good source to confirm the solar energy spectrum point.
Bonus: Indoor Gardening Tips from a Man Who's Very Scared of Plants