Good question!
As mentioned a bunch already, flouro = transparent.
Lay a heavy % base below, and the overprinted result can suck.
Lay a low % base below and it sucks less, but it's not the look you were after.
*I made a custom 'hot pink', by eye..think 80's hot pink, with some underbase printed below it really jumps off darks.
I did something similar with wilflex's blacklight green as the foundation and added some bright tiger to increase opacity.
Adding white turns it pastel if you go overboard, but there's a fine line in there someplace that seems to work.
I don't have any mixture formula though.
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