All the evidence points to bishop II being a human.
That being said yes the can dye android blood red if they wanted too,but you can tell bishop II has human blood and felt pain.
I would also like to note that androids are not as durable as a humans are in some cases(as stated in the Colonial marine tech manual section on androids)Since their bones are made of carbonfiber and their muscles are made from Silicon.Yes they have enhanced sight,hearing,speed and strength but they cannot function if a certain amount of damage is given to them or if they are exposed to space for too long.
Only the later military androids have armor plateing attached to their bone structure.
