[Heroka Vendile]

"Bluies" is the most common Imp Guard nickname for them IIRC, they have a grey-blue skin tone.
And yes, red blood, which is what Orks have too - and not just to avoid dead Orks looking like burst gooseberries (a statement I'm dredging up from the depths of my memory that i once read in white dwarf some moons ago).

EDIT:
Okay, just checked my 1st Ed Codex:Tau properly and there is no mention whatsoever of blood colour - not even in that narrative description of the bonding ritual.