Alright, I’ve made some patterns for Photoshop.
Halftone.zip includes 4 .PAT files:
Red, Green and Blue all contain 4 patterns: Cyan, Magenta, Yellow and Black.
To use, put them on layers above one another, and set the blending modes on all the layers to darken. When viewed from a distance, they should be seen as whatever colour the set is.
RGB.PAT contains Red, Green and Blue all in one file.