When I started out (a few months ago) I bought a 'bargain' 4lt tin of olive oil because I'd run out of the one in my pantry, and it was a dark green - something I couldn't see before I bought it since it was in a tin. It definitely made the soap darker so I stopped using it and went back to the one I'd previously used. It's marketed as 'light in taste' and is certainly a lighter colour. Other than that I generally use palm, coconut and castor, sometimes adding Shea butter. All of these are pretty light, and I can only get what I can get, if you know what I mean - they come from a supplier. I've just cut a slice of the soap I made yesterday, with TD and activated charcoal (and a really pretty gold mica swirl on the top which has chasm-like cracks all through it!) and it's crumbling. I don't think I can even use it for anything. I won't be messing with the lye concentration again