Ok, human blood is iron based, hence the red.
Vulcan blood is copper based, hence the green.
But what in the galaxy is Klingon blood based? I have seen it range from neon purple to Pepto pink. What element would give their blood this purple/pink color?
It's concentrated rage (purple) and concentrated evil (pepto-pink)
Lead maybe. I remember some experiment we did back in chemistry in high school where one of the chemicals we were mixing was lead and it turned the solution we mixed pink.
I feel the need to stray from topic and bring up a funny thing that happened to me. I had an Aunt that was a teacher at my High School, specifically Honors Science. Well, we were doing a really volatile experiment one day, another one of those color changing dealies you spoke of.... only thing is person that used by beaker before me never rinsed the detergent and residue from the last experiment and it mixed with the new chemicals. Instead of turning the expected blue it went Mountain Dew Green and fizzy, then combusted.