Yipes alphabet wallpaper! Maybe you could convince your parents to help you take it down and then paint? I probably wouldn't paint over wallpaper either, but you can get it off. Then when you paint, go for a neutral or at least pastel color - something your parents won't hate, and they wouldn't have to paint over when you get older if you move out and they turn your room into a guest room or whatever.
If you're having trouble convincing your parents to ditch the abc's, maybe tie it into school? Like if you get good grades first quarter or semester, you can get rid of the wallpaper? I mean you are an adult now!