Unfortunately, if ya use pink sugar, you're gonna get chocolate brown. Just the nature of that beast because of the high vanilla based component of the fo. You can try all the stabilizers and different colorants that you want, but you're still going to get varying shades of brown. Now since you're wanting a pink top, why don't you scoop out a little of the soap just prior to adding the fo, color it pink and then pour it on the top of the scented soap just after you've poured it into the mold?