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?