You can probably google
RT helmets stripes for better official pictures, but here is a comparison shot I took a bit ago of some of mine.
Basic stripe for a basic trooper.
Parallel lines in a secondary color for vets
Hashed line for sarges
Both parallel and hashed for vet sarge.
With Rainbow Warriors things are going to be more complex, as they have multiple stripes to start with, but you could incorporate the cross hatching for the sarge.
YMMV, just tossing ideas out.