Similar situation: every time i look at the nepenthes thats been slowly getting more and more red, i think to myself that the pattern its doing so in reminds me of blood vessels. Almost as if thats why its called nepenthes sanguinea. I didnt do my research on this species when i bought it, i just saw it was cheaper and more likely to acclimate well if i fucked it up but yeah its definitely the blood vessel plant
As you can see: