Thatts the blog I was talking about.
The third colour is only mentioned in the image labelled "painting guide" where the three colours are dark grey, medium grey and base colour. However in the SBS with the helmet he does only use 2 colours which can be a bit confusing.
However UCP in reality has three colours which are not particularly distinct from each other. See here:
However in this scale 2 colours can be used since the size makes them hard to tell apart, so it is up to you whether you would like to add the third colour or not.
Sorry for the confusion and hope this clears things up a bit
Have you looked at UCP decals? They have a good pattern on them but I have yet to use them.
Anirudh