Ah teal, such an evil color..apparently.
I wonder who decided that and why. I know the the first toy/character to us it was Black Lio Convoy.
Red too, but only as a highlight.
Even the original lucky draw Black Lio Convoy used gold instead of teal, it was the TRU exclusive one that used teal first.
I think it was Car Robots Black Convoy that really solidified it (since it wasn't used on the Black reissue Convoy, Black Fire Convoy, or Black Big Convoy).
But it's used on plenty of the heroic Black Convoys/Optimus too (Henkei, Animated, Masterpiece).