Thanks guys. I'd already stumbled across those R&F sprays, but they're out of stock of the amber at the moment. I'm only really after a subtle change in colour. Just this morning I've cut out the headstock so I have a couple of scrap pieces now to test on. I'm thinking of combing what I have left of the vintage amber with a few drops of the tobacco brown just to give it a little bit of a brown hue. Will experiment with a few combinations and see how it looks.