For a while I thought there was something Zodiac related. Scales and twins were the main ones, and I added virgin in at one point, as well as shell (thinking the crab's shell for Cancer).
I thought for a while about "things with bite". An axe, obviously. The phrase "its bark is worse than its bite". I Googled to see if people would consider olives to have "bite" in the metaphorical taste sense (and yes...they apparently do). I was so confident in yellow that I didn't even look at the actual literal word "bite" to notice that this would have made my idea obviously wrong.
Finally, I spent a while trying to find "things with shafts". The shaft of an axe. The shaft on a typewriter. Google's stupid fucking AI told me hedge mazes' walls can be called a "shaft" (but on deeper inspection, I could find no human who had ever used the word in that way).
Yeah I was definitely surprised that blue was blue. Yellow or green would have made sense, but it jumped out immediately. The only thing I can think of is that it seemed too obvious and like it may have been a red herring.