i love the liquid at gentlemen's reserve! these are what i have tried from them that really seems to do a carto well:
mojito
peach melba
blueberry pie (also blueberry cheesecake is darker, but doesn't really gunk up a carto)
candy caine. i wasn't stoked on the idea of the flavor at first but i ended up loving it. it's a pretty light menthol.
strawberry colada (but this is a meh flavor to me. too much colada, not enough strawberry)
apple cider and caramel apple do well in a carto, but maybe not the lightest.
i feel like i haven't tried enough flavors from them.

btw, the orange creampop is delicious, but gunks up cartos something fierce.