White went yellow.. how to fix?

I have a scene in a sleeve and my white went real ugly.. turned yellow and blotchy and looks dirty! I don't really want color there but would be ok with a light Grey.. Do you think Lt Grey would be a good solution? If not, what do you suggest I do to fix this problem? :) Also have red roses and they are quite dark.. how do I lighten them so they are bright and not so dark and muddy? Any advice would help.. thank you!