I wasn't questioning what they're called, so much as what they do... Which in the Incredible Cross Sections (most current tech material on Star Wars stuff), they (as they often do) do some squishing together of what the purpose of the solar panels are. They don't just collect energy though... They're also listed as having a (in the diagram) heat exchange matrix (IE: a radiator) which makes up most of the panel's bulk, etc.
They also list it having a fueling line and things, which contradicts it flying on solar power completely... or perhaps the solar power feeds something else? Weapons or the argued particle shields people have brought up (due to space debris being an issue for an unshielded ship, blah blah blah).
Like Jeff said, JJ Abrams probably thought it looked neat to photo negative the TIE Fighter, add some greeblies, beef it up some here and there... voila, "advancement of technology in a fairly static technological advancement universe!", and you're done. It could be as simple as the First Order wanting to distinguish itself to the Empire in some weird way?
I'd say the simple answer right now is a "solar panel" on a TIE Fighter is not a solar panel on your neighbor's pool heater though, and thus doesn't work the same way, whatever its purpose may be. And so a white one maybe works as well as a black one, or better even. *shrugs*