It's very interesting how the colors all match together and with the atmosphere of the whole picture and help the figures in the picture blend together. Pretty nice how you've also managed to translate Opeth's lyrical themes and general feeling through visual representations and overlay these with their logo.
One minor thing I wouldn't have done the same way you did it, is just the background. Having it just plain white makes the whole picture look a little incomplete. If you really want to use a light color, going more in cream tones or making it look like some kind of white canvas would be great.
Great piece of art anyway. Keep up the good work!