Sounds like there is a huge range of normal. DS knew red, blue, green, yellow, orange, white, black, brown, and purple before 2 (don't remember exactly when) and now (28 months) does "kinda orange kinda yellow" for construction vehicles and similar.
The one thing I will say that should be kept in mind is this: some (and only some) of the variation in when toddlers know things is about what they are exposed to and how often. DS is 28 months and speaks in 10-15 word sentences, uses words like "actually" quite appropriately and is starting "if, then" statements. He knows colors, can count items (with understanding) to 4 or 5, knows how to get places (as in "Mommy, turn here, let's go to Centennial park and play on the playground"), yada, yada, yada... But, just as an example (I am sure there's more) he has no clue what shapes are. Zero, zilch. We haven't avoided them on purpose, I just don't find hey fit into everyday language right now, so I don't say "look, that sign is a square" so he never hears it. We're also not into flash cards or flash card style board books (just story books). So if someone posted a "does your DC know their shapes" the answer would be no, but obviously its not because he's not capable.
Just a thought, again, I think that only explains a bit of the variations. I really think they all work on different areas at different times, your daughter might be working on a whole other part of her brain than where colors are processed/remembered.