I've always fancied having a go at dyeing but never got around to it - but finally decided to take the plunge and have a go with some food colouring:
I used red, yellow, green and blue, painting it onto the yarn which I had previously soaked in vinegar, then I "cooked" it in the microwave.
I was really pleased with the final result!
However when I came to knit it up I found that where the colouring had "pooled" at the bottom of the bowl I had created a kind of dark brown, which appeared as blobs in the final result when knitted up:
Ah well! Beginner's error I guess. It was great fun and I will definitely try again, though I might pick just one colour next time!!