last working version: 184.108.40.206 (I skipped .10 and .11)
When a person joins a group or zones in, the bar color defaults to white. Reload doesn't fix it but I think getting into combat does. During combat this is not a problem. Notice from the image that some class colors are fine and the 2 white bars that aren't pointed out are correctly showing priests.
I've seen this in raid and 5-man on my priest, druid, paladin, hunter (the only ones I've tried. I assume it will happen on all classes)
When assigning colors to various debuffs, I like try to use similar colors for different encounters. For example, for a low priority "hey heal this" i use pastels and higher priority "uh-oh" I use something a bit more saturated like lavendar (Buster cannon for instance) and "oh-shit" fast reaction debuffs I like something fluorescent like chartreuse or bright yellow ( Hex of Lethargy, Gigavolt Radiation.) It's never exactly the same color (tho I try to click the color wheel in the same spot) but I always hover around trying to choose a good color that's not too close to the class colors and prominent enough to get my attention.
Now if I could create my own palette of, say, a max of 8 colors that are favorites and I can click a swatch instead of some random place on the color wheel, then I can get this done so much faster AND train myself better to react to specific colors. Cuz if I have too many choices I take a long time. But I (not you guys) need to be able to make the palette, or maybe you create a default palette that is editable.