No, nothing to do with Valentine’s Day. I’m talking about how your characters see the world.
Violets were actually “blue” for a very long time. While violet as a plant goes back to Latin and older, the first time we have “violet” recorded as a color name is in 1370. We know people could see violet as a color just fine; heck, we have violet manganese pigments used in cave art at least 25,000 years ago. But what did they call it? We have no idea. Languages differ in what colors they admit exist, and how they carve up the spectrum of visible light. Scholars of color and language find that white and black come first in any language, usually followed by red and a plethora of others; blue is one of the middling colors recognized, and purples come even later than that.
This will affect your world in subtle ways that may be hard to convey through text, when you have to use your own modern language which does have blue and violet. Think of Homer’s “wine-dark sea”. The Greek of the time might split colors into yellow/green as one group, and dark green/blue/purples as another. So we don’t know what color Homer actually meant the sea was – and as people who have visited the Mediterranean have pointed out, sometimes light and waves mean the sea really is kind of purple.
Another possibility is that your characters aren’t standard-issue human, and don’t distinguish violet as a color at all. That probably means their ability to perceive red is off; while humans do see violet as a color in itself, we also perceive violet when what we’re seeing is blue light mixed with a bit of red. That will lead to its own set of knock-on effects, changing what works as effective camouflage and just how garish outfits may be to outside eyes.
Of course, the final reason violets might be blue are that the violets are actually blue. Where I grew up there were two common types of violets in the woods; a small, mostly white one and a larger violet one. But where they grew together? Every once in a while you’d have a stray plant whose flowers were a slightly streaky denim blue.
Not violet. Blue violets.
The world is sometimes weird that way.