I'm trying to find the right word to use for a stripe in Jiu Jitsu; as you go up the levels you receive 4 stripes per belt colour. Would I use 'rayas'...?
Raya seems to be appropriate for this context, like
En el segundo nivel el cinturón es blanco con una raya naranja
I was surprises first time I was told that there are more levels beyond a black belt. I think in karate they are called dans. Probably other disciplines have their own names as well as their own color schemes for belts, but AFAIK, there is no specific term to describe these stripes.
I just google for some info and found the following table, which again uses rayas (example for the 7th Kyu) to convey stripes:
Nevertheless, take notice that the above is appropriate to describe the belt to some one, like me, who has no idea what it looks like. People who are already "in the business" and know what the belts looks like often refer to them as "blanco, blanco-amarillo (no mention to the stripe), blanco-rojo, etc.)