Ol'Wonky is a old man that may tell you something that may help you.If you talk to him he will tell you something for 5 coins.(Ol'Wonky is in rougeport sewers in the building net to the shop.)He will tell you the subject of the thing he's going to tell you before you pay.One of the subjects is "Yoshi's Colors".In some part of the story he tells you "a yoshis color depends on the condition of the egg before its hatched.

PS.If he tells you that story meanwhile you have your yoshi out he will say theat your yoshi has a prety nice color.