Olly, they are referring to the Reflex Springs. The 13.5lb spring we offer is indeed also known as "yellow". This is a Reflex thread, so the questions are pertaining to our brand of hop-ups.
Bosco, on our set-ups with the RSD TC6 pistons, we have been running 400-450cst rear and 500-550cst front.
On another note, I want to also take this opportunity to thank Jeff Cuffs for giving Reflex Racing and RSD our very first ROAR National championship!!! Way to go!!!
I saw on some pictures that Keven H. was running our springs. I wonder if Rick was too? He ordered a few sets a couple of weeks back. Could it be 2 National titles perhaps?