Trolls and the color candy red
Karkat is a mutant with candy red blood
Terezi’s eyes became candy red after getting scorched
Every time Gamzee has lost it he got weird red eyes
Here’s what I think
I think there’s a candy red chemical that exists in their eyes that acts a bit like tears on steroids.
Tears are supposed to clean out the eyes and also tell other humans “Hey. I am not ok. Please help.”
This weird red chemical is meant to be an indicator for damage, like bruising for only sensitive areas
So here’s what I think
Gamzee’s rage coats his eyes in this substance, clearing out anything that would disrupt him and gives him tunnel vision. The massive stress from his rage brings this chemical to the surface, allowing it to do it’s job, but also brining the eyes close to injury from sheer physical stress.
When Terezi stared at the sun the gland that produces this substance cracked, popping like a blood vessel, the substance crystalizing onto her eyes from the harsh heat and light
Karkat’s mutation makes his blood the same color as the substance. It appears that he is severely injured and his blood is basically a big red sign saying “My entire body is very sensitive” and thus making him a target for culling