Which color is Orc blood?

I would be careful about using science (specifically chemistry, or to be even more specific, inorganic chemistry) to describe the color of blood. It's true that human blood is red because of the iron ions, but it's more than the iron itself; the ligand system to which it is attached (the porphyrin) in combination with the iron ion provide a energy level gap that happens to fall within the visible light region we consider red.

As such, changing or tuning that metal-ligand system can can affect that color. The ligand's electronic properties (and thus the color of visible light you'd see, if any) can easily be changed with some organic chemistry. Changing the metal ion can also affect that color; lobster blood is bluish because it uses copper ions instead of iron ions. I'm sure there's a metal-ligand arrangement that results in a green color that would also be fine for transporting oxygen and doing all the other stuff blood could do for an orc.

Anyway, not knowing what the official word is, I'd prefer orcs to bleed red. Red blood is very primal and definitely evokes that basic primal instinct of killing. Doesn't have to be bright red, just some kind of red.

Note: It's been awhile since I've reviewed my chemistry. I could very well be making that all up.

I was looking through my old WDs last night, and found a bit of fluff which mentions 'black blood flying everywhere' (I think that was the words, definetly black blood) while SMs shot Orks.

Ork blood (in 40k) is indeed red. There was an official article on it a few years back citing that the increased iron and oxygen in the ork blood makes it a deeper red than human blood. And it is the 40k Orks that are propogated from fungus.
Originally, the WFB Orcs were derived of similar means (fungal based) however I believe that latter versions of the official story have changed over time, and for the WFB Orcs there has been less and less mention of the fungal theory and more, subtle, emphasis placed on more normal breeding measures.
Regardless, the blood of Orcs is indead meant to be red, and if I remember correctly (at work so don't have my WD's etc to go through) that this is for 2 main reasons. 1) That Orcs are more aerobically active and athletic than humans, and a higher haemoglobin count (which is meant to bond the oxygen or something - been a while since I studied Biology so forgive me if my terms aren't 100% correct) means that their blood is a deep red colour, similar to humans if not slightly darker/deeper. and 2) Because red blood looks so much cooler than green blood. It stands out more and is easily identifiable. And yes, these 2 were the official reasoning behind it.
For the photosynthesis side of things, I believe that this was to do with the rapid clotting and healing factors naturally inherint in the Orks/Orcs, which allows them to continue fighting effectively with debilitating wounds that would otherwise see a human completely incapacitated, and to also explain their 'toughness' and ability to survive horrific wounds/procedures with minimal side effects (other than the missing limbs etc).
As to the Eldar bleeding green, I have never heard of this before? Where was this from?

Exarch Thomo - With the Orc biology thing: it's the other way round! They used to be breeders and the latest edition of Warhammer Fantasy hints that they are sporing.

I've always imagined it as a very very dark red, on the point of being black.

WarbossKurgan wrote:

Exarch Thomo - With the Orc biology thing: it's the other way round! They used to be breeders and the latest edition of Warhammer Fantasy hints that they are sporing.

Really? Hmm, ok. I must admit that I am only a relatively young un and came into fantasy during 5th ed. and I haven't even looked at the latest Army Book. So they are moving towards the spooring thing in FB hey? That's a shame, while it is great in 40k (easy way to explain massive waaghs) I don't believe it works for the fantasy setting. And I know where I can get a hold of the old orc cheerleaders from Blood Bowl to prove it.