I'm really interested in have a good system for letting the user have optimum control over multi-color fonts. The professional designer needs control over each layer, each gradient. The amateur needs a supply of preset palettes with friendly, multilingual names. Both need a simple way to coordinate more complex palettes with existing color schemes.
If you have a 2 color font, the user sets each color...no big deal. But what about when a font has 20 colors. Like a metallic effect with two different metals used for the same letter...intertwined silver and bronze. It's not a simple light to dark range, there's some hue and saturation shift. Each material requires its own sub-palette so if can be modified discretely.
Unless the professional designer is well versed in rendering metals, manipulating individual colors would likely result in a mess. If sections of the palette could be provided as morph targets, the user could change the bronze into steel, the silver into gold.
On top of that, the user needs to be able to have control over each palette section. Hue, saturation, gamma, luminosity, alpha etc.
Without all of these things, color fonts are useless for professionals and impractical for amateurs. Right now, if an amateur has an application that supports multi-color fonts, they need to install multiple copies of the font, one for each palette. I think about 100 palettes is the bare minimum I'd want to provide to make the fonts even a tiny bit useful. Delivering 100 fonts (for each style!) and having the user manage that is ludicrous.