rainbow granny square + pom pom

I'll admit straight up that the colours aren't me, they are miss bells (at the moment, she is 5).  Rainbow colours - she loves to draw rainbows, paint them, make necklaces with the repeating colours etc. etc. etc.  So I thought I'd attempt my very first granny square in her favourite colours.  I can see how people get a little addicted to making granny squares, I think I'd have to do it in natural colours though, I can't do bright BRIGHT!  I do have some linen yarn, it is quite thin though - it's the yarn I used to make my crochet shopping bag - they'd be quite small granny squares.

 we could just call it a mat for her rainbow pom pom...