Cheers. I was going to make the stripes in separate batches. One blue, one white, and then lay them on the cake separately. Hopefully that should stop any colour bleeding.
Yep never paint food colouring straight onto ready to roll - it'll bleed continually...
There really isn't a quick way around it using ready to roll instead of kneading up batches of colour first...you can dampen the icing with a light spray of water and sprinkle on colour dust, but thats pretty tricky too as it can bleed as well, but does make a nice different style if you're practiced at it...