“The Simpsons” is giving one lucky contest winner the chance to make others yellow with envy by creating a character for the TV series. The new Springfield resident will appear in a 2010 episode featuring Chris Martin of Coldplay as guest star. The contest, part of the Fox show’s 20th-anniversary celebration, is for those 18 and older. It opened yesterday and runs until 11:59 p.m. EDT next Saturday.