Imho, this add-on is pretty cool.
The visual difference between the stock standard XF prefixes <vs> the customized prefixes this add-on enables—is quite noticable, and there is no doubt the customized prefixes definitely look a lot better than the stock XF prefixes.
I mean, obviously they're still just prefixes, but the 'Custom Colors Picker' add-on allows for optionally customizing up to 3 separate colours as well as optionally adding any of 4 types of font awesome icons too.
Tbh I reckon stuff like this ought to be integrated with the XF systems as a standard.
Regardless, [XenSoluce] 'Custom Colors Picker' add-on gets the full 5/5 stars from me.