The best book I know for starting to understand coat color genetics is the outstanding book
ABC - About Bunny Colors by Ellyn Eddy:
https://rabbitsmarties.com/product/rabbit-color-genetics-bookhttps://www.allthingsbunnies.com/ABC-About-Bunny-Colors-p/bks107.htm
In common English, not "science-ese," it takes you from the basics of how Mendelian inheritance works, through the five major gene series that produce rabbit coats colors, plus several additional series (Dutch, Vienna, Silver, etc.). It has color charts that I still refer to after years and years of studying this topic. It also has a handy color translation chart, helping you understand, for instance, that chestnut, copper and castor are all the same color genetically, but called something different in different breeds. It's really a great start, and will make all the other resources, especially some great ones on the internet, comprehensible.
@ladysown is right, that silver marten coloration means the buck is probably not a full New Zealand (although I've had very interesting colors pop out of NZ Whites when I bred them with Blacks, Blues or Reds; I've found NZWs often carry steel or chinchilla).
As far as fun colors, harlequin might all you need.
That
e(j) allele can mix things up and keep life pretty interesting! Breed him to your broken doe for possible tricolors. Agouti does (chestnut and chinchilla) can give you more harlequins, and also harlequinized agoutis.
The silver marten colored buck - which has a tan allele
a(t) plus a chinchilla allele
c(chd) - can be crossed with an otter or a chestnut. If the otter carries chinchilla, you'll get otters and martens; if the chestnut carries chinchilla, you'll get chestnuts and chinchillas. Either way, all his bunnies may inherit the tan and/or the chin. He may also be hiding a self a behind his tan
a(t), which means yu might get selfs if you bred him with a black, blue, chocolate or lilac. And there are any of three other possibilities (shaded
c(chl), himalayan
c(h) or REW
c) behind his chin
c(chd). Breed him with a REW to see what they are.
If either of the bucks carries a REW c behind his dominant allele (which is full-color
C in the harlie and
c(chd) in the silver marten), breeding him with a REW will probably give you some white bunnies.