Your comment inspired me to experiment tonight. I made strawberry flavoured marshmallows tonight and instead of plain cornflower I cut it with icing sugar & unsweetened cocoa. The finish isn't as 'soft' as just with corn starch but it was tasty!

ETA: Ok, that didn't work so well. I just checked on them (well, ok I was going after the rest of last night's lemon-ginger marshmallows!) and they'd all started to stick together. The cocoa & icing sugar had soaked into the marshmallows & started to get icky. I've dusted them with corn starch & hopefully that will remedy the situation.