Primary condition in vanilla system is that given armor piece is a witcher gear quality (quality 5 in xml).
Beyond that the armor texture needs to have pure red and/or pure blue parts on diffuse texture (those will be replaced by color shift 1 and color shift 2 hue shift values).
Entire area that has red/blue elements has to be masked in green channel of ambient map.
Then entity setup has to be made similar to other witcher gear armor entities, XML points to one entity which holds all appearance templates with respective color shift values, whilst appearance template entities point to actual armor mesh.