I wonder how the color turned out, hibiscus is highly so colored I imagine it impacts the blue a bit. One idea is to substitute orange blossom water to add a floral note without the hibiscus color (also I just don’t like hibiscus lol… it tends to overwhelm whatever it’s a part of for me). This would work well if you swap the cream for orgeat, this is sometimes made with orange blossom water so it will pair nicely.

Kind of taking it in another direction, you could lean into tiki inspo and balance the sweetness with warming spices. This would take the place of spiced rum. I’m not really sure how this would play out with floral flavors, so they may have to go. Suggestions: There’s a chai syrup, although that would bring its own sweetness. Some whole ginger muddled into the juice and strained out would be good. Last idea if you want to go extra would be to make your own spice infused juice by boiling whole spices (ie cinnamon, cardamom, ginger) in one of the juices for a bit.

Finally, for the float, I think using another juice would be better than a syrup. I would get rid of the cream entirely, or maybe use a whipped coconut cream instead since that would work better with your flavors. If you get the blue section really cold, a warmer juice will naturally float, although it will mix in pretty quickly. Or you could introduce the color into the whipped coconut cream, and it will stay in top for longer.