Risograph inks are soy-based and do not conform exactly to any color standards. The listings below are approximates for reference only. Additionally, Riso inks are also slightly transparent and allow for variations in overprint and based on the color of paper they are printed on. 

Two historic RIPS

In an attempt to clarify the compatibility of RIPs (Raster Image Processors) with their respective RISO models (mostly duplicators), this list can maybe be of help.

INK color codes for MZ machine.

Very useful to rename custom color drums !