After seeing this blog post, I dug out a very old stash of pale cream coloured pure wool (probably around 20 years old and never used) and some food colouring I had in the back of the cupboard and first made this -

The top ball was using the old food colouring from the cupboard, then I bought another box of 4 colours the next day and dyed the second ball. I don't know if the difference was just that the first batch was old colouring that may have started going off. The bright mix will probably end up as a jumper for my niece.
A few days later I found separate bottles of food colours in a different shop, so got a couple of bottles of blue and red to make this batch for me -

And I tried some older dyes I had bought for cotton fabrics, but hadn't used because I found on the instructions inside the jars that they were wool dyes.

They were both supposed to be rainbow mixes of turquoise, red and yellow, but most of it washed out and left one ball as a light mint and the other as a peach colour.
Now that I've used up that old stash, it's time to go looking for some more mess!