The problem is that, even though you're using non-greedy matching, Perl still works from left to right, return the left-most longest match that satisfies your regex. If you'd done s/:.*?// you would have been left with "fruitred:apple", but since you have s/:.*?$//, Perl needs to match "end of string", and the .*? then matches all the way from after "fruit:" to the end of the string. Using non-greedy matching and the $ anchor won't get you the result you expected; you'll need to use a more specific regex like s/:[^:]*$//.

Also, the /o modifier is utterly useless here.