I found that using a glyph is more colour efficient if you manage to score a hit.
I used wasp on one of the three flying monsters in the nameless garden and only needed ~8 drops (tanked up on crimson) to kill it where I normally need about 14~16 to kill it with just raw colour.
however I also found that (at least wasp) is rather flaky in scoring a hit.
If you manage it right and the monsters are close together you can knock all 3 out of the air with roughly 10~15 drops in that level due to the explosion (can't give precise numbers here since a you can imagine the chances that all 3 are close enough together are remarkably slim and I only managed it once in waaaay to many attempts)
But there is a good chance that the thing just flies on and hits a wall doing sod all damage where raw colour always hits from what I can tell.
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"Weaseling out of things is good. It's what separates us from the other animals....except weasels" -unknown
All those who believe in Telekinesis raise my hand.