Sixteen inks and no house style
A house style is a way of not deciding. A library is a way of deciding sixteen times.

A house style is a way of not deciding. It is a decision made once, in a mood, then applied to every problem that arrives afterwards regardless of what the problem needed. That is efficient. It is not design.
Instead we keep a library. Sixteen Risograph inks, each of them tested against paper and against type, each of them with a measured contrast ratio written next to it. Nothing enters the library on the strength of a screenshot. It has to hold at eight point, it has to survive a second pass on the drum, and it has to pass AA against both the paper and the ink.
The library is on this site, on the colophon page, with the contrast figures computed live rather than typed in by hand.
The result is that every project in the book is a different colour and none of them is arbitrary. Salt & Ledger is teal because the archive it draws from is printed on blue-green ledger stock. Ninety Proof is orange because the label sits behind glass under warm light and everything cooler than orange dies there. The reasons are boring, which is how you know they are reasons.
The library is on this site, on the colophon page, with the contrast figures computed live rather than typed in by hand. If one of them ever fails, the page will say so.