Slight browning on piston

[toppers]

Brand new Echo 7310, runs very rich first few tanks. No gunk on exhaust port or muffler. Ethanol free 45:1 red armor is the fuel. Notice some very slight browning on top of piston after tank #2, what could cause this? It's very miniscule but just curious as to what it could be. Also, no babying or long idling practices here...proper warm up then all sorts of dynamic (high) loading on break in.

 

[82F100SWB]

Sounds like normal operation to me!