Yes Methylated spirit has a Blue-Purple dye added in most countries, this will fade in the sun. Filtering though activated charcoal is a good efficient way to remove the dye but I just look for simple and what's on hand
Yes I do use De-waxed Blonde Shellac, as well as Lemon, Button, and Garnet. sometimes you need to add Tumeric aor Dragon's blood. Tumeric is added to shellac for varnishing brass work. Dragon's blood is a red resin pigment made from plants, it's added to shellac to give a reddish finish. I've partially restored a Butcher Whole plate camera that had an opaque distinctly reddish finish, it's just waiting for bellows, and has been for about 3 or 4 years. I used Inkjet pigments to get the right colour match and it worked well, I should buy some Dragon's blood though
Ian