What color will plants go toward?

Answer 1

Phototropism is itriggered by light between 350-500 nm, the blue region of the spectrum.

Mustard (Sinapis alba L.) respond to both the blue photoreceptor and the total amount of light within the hypocotyl.
http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-3040.1987.tb01610.x
Boergesenia forbesii, a green alga, has negative phototropism. The minimum light energy inducing the phototropic bending was 467 nm and maximum was 502nm.
The bending was at a peak with 380 and 443 nm.http://pcp.oxfordjournals.org/cgi/content/abstract/20/5/983