In reply to ClimberEd:
> Ah, now that's interesting because I think for most competent skiers skiing really starts 'beyond the runs'.
> Anselme Baud's 'mont blanc et aguilles rouge a ski' (aka 'the book of death') has a grading system from F (facile -easy) to ABO (abominably difficult, although I think these are only suggested and skied routes stop at ED+) wrapping a number system from 1 to 5.
> F is basically a red run but off piste.
> So maybe up to red run is a bit like scrambling/vdiff, black run is VS and onwards from there.
My take on it is that most occasional recreational skiers will, once they've become confident in the basics, spend the majority of their time doing blue and red runs, while anyone with particular drive or talent will very quickly progress beyond that level. Certainly there are many people who have been skiing many times and still would be reluctant to even try most black runs even in good conditions.
I'd put red at around VS, just above the level you'd expect most absolute beginners to be able to do on their first forays (i.e. green Diff to blue Severe) but far from out of the question if they took to it well. Then black would mean HVS, although the variability of conditions would mean it often would feel harder. In sport grades I'd put red at around grade V moving to black from 6a or so.