How to remove oil pastels?

i just did a great picture of albert einstein using oil pastels, but im an idiot because i did it at night time and the light was dim, when i looked at at the next day he was alot more yellow than i had planned him to be, is their any way at all to remove the colour or thin it out so as i can lay down a better skin tone? i know once you blend pastels and put down a layer if you try to put another colour over it wont grip the paper and it becomes a bit of a mess but surely there must be something i can do? any help would be great thanks