Tiny, the background that he was on in the original photo was red dirt in outback Australia, I didn't want to draw in red sand in detail, but he looked 'lost' with no sense of ground without something other than blue, so I just threw a few colours into the background ;)
As for sizing, well I go by 'A3/A4 etc.' just to make it easier to word, but have the exact measurements on my website. Basically in an advertised 'A3', the portrait itself will measure 15x12 inches, or 37x30cm.
I am currently working on my next commission, which is an A2 graphite piece of a horse's head and partial body. Will be keeping me busy for a while I think!