In Chrono Trigger, one moon exists, its colors ranging from pale yellow to red (seen from suborbital elevation on the Black Omen).
In Chrono Cross, two moons exist; the second one came into existence when Dinopolis was pulled into the Keystone Dimension. Apparently, the moon of the Reptite world was pulled with the city. It is a crimson color. The moon indigenous to the planet has strangely changed colors to pure white in the game. This is likely a developer oversight, though it is possible that volcanic ash or other smoke in the air caused this effect.
In Radical Dreamers, the one moon is ostensibly the pale yellow color from Chrono Trigger.