how many colours does Photoshop have?

I'm slowly working my way through the Photoshop Elements tutorial book (onto lesson 5, all about selections), and thought I'd put what I'd learnt to use to check out some possible colour combinations for the background of John.  I'd already painted dark green graduating to white, which didn't work, so thought I'd have a go virtually.  I don't want to do any more to the portrait itself yet in terms of playing with colour, tone and the like till I've sorted out the background.  So, here are 6 versions.  I'll play with graduating it to give it depth.  Currently tossing up between blue (with some Darwin clouds perhaps) and lilac.  Mmmm.