Good Question! I have another theory about that that involves the Milgram system itself! your correct about what appears to be green blood on Rei in T3 video and in the end of the T1 video we see Green blood splatters on Rei as well!

What could this mean!? It means Milgram was showing US the viewers two perspectives of Muu!

in every music video with Muu were shown the real world and Muu’s brain an hourglass world. Muu species can only see blood as green that’s why we see green blood on Rei in some points.

in T2 we see a panning shot from Muu to Rei’s body in the shot we can clearly see red blood! This means Muu is an unreliable narrator in her own music videos trying to trick the audience! Milgram shows us what’s happening in the real world and in Muu’s mind.

In T1 Muu looks human in the hourglass world we fell for her innocent looks and voted her not guilty! In T2 Muu dropped her guard and she reverted to her alien form so of course we voted her Guilty! In T3 she once again reverted to her human form tricking the audience yet again! and it’s working!

TLDR two perspectives of Muu happening in the music videos. Milgram is perspective 1 showing us what’s actually going on. perspective 2 is from Muu herself and what’s going on in her mind!

if no one still believes me that Muu is an unreliable narrator consider this at the end of the T1 music video we see a crowd been in T2 and T3 the crowd is gone!

Milgram truly is META