Your transmission tuning is a big deal. If you are running a soft, or weak center spring, your transmission is changing too fast. The yellow is an awesome spring for most sport setups. This could be the difference of pulling wheelstands off the line, or your bike being a total dog until 15mph. I've seen it all too often. The yellow is a 30% stiffer spring, and is best for higher rpm bores. The next step up is the red 35% center spring.
white is the softest, yellow is medium, red is for race application!