@lithelight and I were discussing the topic of glowing blood and it reminded me of some 2012-era headcanon blog post about troll blood glowing the higher up it is on the spectrum

and i’ve always dismissed it as a pretty silly idea but i think if you view it from an angle of being like… a warning sign? like in the sense that something with luminescence is really obvious in caves and nighttime environments where trolls spend all of their time, then i think like

if you can assume, for the sake of the headcanon, that at first all troll blood had a very visible glow when it reacted to air, then it seems likely that lowbloods over time would have bred the glow out for the sake of their own protection; an injured lowblood is an easy target, and to have a trail of blood so easily trackable through a cave or through the night would be a really huge weakness.

highbloods, on the other hand, get an advantage out of it; because everybody knows a highblood injured is more likely to be angry and dangerous than any kind of vulnerable. because of this, a highblood who might be severely damaged and not actually any kind of threat still gets the advantage of having a trail of ‘stay the fuck away’ leading behind them, which gives them a chance to lay low and have their highblood biology deal with the problem. even if a smarter troll might decide to stop and actually take into account the amount of blood visible, the fear factor behind glowing purple is still there.