Moon light sensor

From Science:

Moonlight triggers the synchronized spawning of reef-building corals; however, the mechanism underlying detection of moonlight by these animals is largely unknown. Levy et al. (p. 467) now demonstrate the presence of ancient blue-light-sensing photoreceptors, cryptochromes, in the reef-building coral.

I think this is cool. However, how these photoreceptors distinguish sun and moon lights? Sun light must also contains blue color that the moon emits. Maybe the photoreceptors are only expressed during night.