Removed anodizing from a canti hanger using the following technique from Jez (as above though, disclaimer if it doesn't work, I wasn't too worried about the canti hanger although the outcome was fine)
1) Get caustic soda - I got mine from Tesco
2) Use a washing up bowl or similar plastic container
3) Put warm water in container (probably should not use hot water, may acelarate the chemical reaction although could be good for Fight Club style chemical burns)
4) Water will fizz so don't touch it (unless you want the Fight Club burns).
5) Stick the stuff that you want to clear of the anodzing in the container and stir with a wooden or plastic spoon (probably best not to use a cooking spoon). Should now be more fizzing and you should start to see the colour being removed although speed will depend on strength of solution - if in doubt start weaker.
6) Periodically check by removing to see how it's progressing.
7) Some alloy componentry may go black; this is just a top coat of crud that just needs rubbing off.
Once all the colours out use a metal polish to buff it up.
And that's it! It probably is best to test a small area or unloved component first.