Consider the purple as the "pre-run color" and don't worry about it. Btw, when you get to 60 size planes the TH 75 is one the best around. Only $5.00 more than the 60 size, has the same mounting, runs great, easy to adjust and has gobs of power. ITs the only engine I buynow for 60 size planes. I have an OS 60FX which runs smooth but is weak in power compared with the TH engines and very expensive.