Hi Steve if one of the colours is a black or dark tile it sometimes makes the wall look 'zebra', like! As robbo says , random is good but do it to the customers spec or they come back and ,'I would have put that tile over there' etc. Either lay them out somewhere so the customer can say yes or no or use this site
IanSharpe.com - Using Excel to produce random tiling patterns Very good because you put in no of colours, and length and height of tiles and it randomly gives you a pattern. Tip, if you see one you half like print it off because there's no 'back' button! Didn't work on my pc for some reason but got it to work on customers!!