Here's the number of different types of quests in the (base)game:
Main quest
Zone story quest
Fighter's Guild quest
Mage's Guild quest
Daily quest
Misc quest
Of all these, the only type that gets a different color are the daily quests, and all quests turn white when you have that quest selected, for 3 total colors.
I'm guessing PC (as usual) has an addon to remedy this, but why was it designed this way in the first place? Why aren't zone story quests given a color, like green, so people don't have to guess which quests they need to do to finish a zone's story? It's not like this would take Zenimax much time at all to add, so what gives?