I've got mountain mix but don't use it on its own as I don't really like the colour so I end up adding other colours to change it up or down. I don't see the point in buying it specifically just to change it. Might as well mix up a colour I like from the outset. My favourite mountain I did was using alizarin crimson (despite red being a foreground colour) with tiny bits of darker colours randomly mixed in, just whatever happened to be on the palette and I got a result I liked. I don't see the attraction to using blue all the time for mountains anyway, other than to help push them back into the painting, but other colours can do that too. I think bob created the mountain mix as a guide, to help beginners so they didn't have to struggle mixing. What I find odd is the colour he mixes in his tutorials for his mountains always seems to be a lot different to the mountain mix he created for the purpose.