Having successfully managed something approximating to a square with one colour, chunky wool and a big hook, I went out and bought some DK in three different coulors, and settled down with a 4mm hook. So far I have made three tri-coloured squares, each neater - but also smaller - than the last. That's the first one at the top, the second on the left and the last on the right, but the perspective's a bit squiffy. If I can stop the increasing tension here, that will be perfect, as the last square is bang on 6". That means I will need 72 of them to make a blanked to cover the top of the crossbed (or go under the mattress). The current plan is to stick with just these two designs of square, and join them with cream, although that might alter.
So, crochet away!