Since you asked, here's a quick(ish) genetics lesson on Harlis.
There are 5 genes that code for rabbit color (plus some others that define white spotting, as for Dutch or Brokens). Those five gene series are A, B, C, D, and E. Each series has at least two options, and every rabbit has two genes in each series (which can be the same option or not). Only the most dominant option will show through, but whatever the other option is, it is "carried" meaning that it can be passed to their offspring, and it might show up if the other parent has the same gene or one which is less dominant (recessive).
The gene responsible for harlequin is in the e-series, written as ej, and is only dominant to e (which is responsible for the color orange on an agouti rabbit, or tort on a self rabbit, as determined by which gene they have in the A series). Sorry that's so confusing...not sure how else to put it.
Anyway, most harlequins are aa (solid), C- (full color), ej and ej or e. (B and D simply determine if they're black, chocolate, blue or lilac). So a black japanese harlequin will be aaB-C-D-ej-.
Magpies are the result of not having the fully dominant C on the C series. In particular, they get the cchd (or chinchilla gene), which makes any would-be red fur come is as white. That's why you were able to get a magpie out of two rabbits which weren't harlequin at all--one must have carried ej, and the other carried ej or e, and the non-rew must have been Ccchd (since the rew could only have been cc).
All harlequins (japanese or magpie) are solid rabbits, although it's possible to have agouti ones.
Because the genes involved are all recessive to some degree, you can get harlequins out of rabbits which are not themselves harli.
If you breed an orange to a black japanese harli you get this cross:
A-B-C-D-ee (orange) x aaB-C-D-ej- (black jap harli)
which will most likely result in agouti harlequins, unless the orange carries tort (would be Aa), in which case you would get proper harlis. If the harli carries tort (would be eje), you could get reds. And you would get torts if both carry tort as described. There's lots of other possibilities if either carries chinchilla, sable, seal, himi or rew (all C-series genes), but one would hope that none of those genes are hidden under either orange or harli.
Sorry that's so long, but I'm a bit of a nut when it comes to genetics...
