green is not a color pigment that exists in cresteds, but sometimes you get a combination of other colors that makes the gecko appear green at certain times. at 2 days old the gecko you saw is not showing its adult coloration (that takes anywhere from 3-9+ months), but it's odd that it would look green and yellow at that age.

i wish i could see a photo of it so i could see what's going on there. did it just have highlights around its eyes and cresteds or was it a flame or harlequin? what about its parents--do you know what they look like? without seeing them or a photo of the gecko itself its pretty hard to say how it might turn out.