I always use color icons to highlight critical keys on my 12 slot bars. The overwhelming majority of icons eq offers are pics, I ignore all of that pretty eye candy. I search out for the few that are closest to solid color, ie the dark red heart on a dark red background with white letters is perfect. Man how id love solid dark black, blue etc icons that I could use to highlight mana regen bandolier buttons or once every 24 hour useable discs .... To me this is a no brainer, eq gives us 1000 pretty useless icons that I never use while what I would [ solid colors ] they don't. These icons with titles on them would stand out on our 12 slot bars ie green for heal, red for attack etc.
I'd love it if they made a series of icons that had a dark background and brightly colored borders. I don't need little pictures on my hotkeys that obscure the text...I need things that actually HIGHLIGHT the key.
You can always take one of the tga files that contain spell/effect icons, find some icons that you are pretty sure you won't miss and replace the icon with solid color square. Drop that tga into your custom ui folder.