I run commercial fuel, and expect a clear to honey colored exhaust. I suspect you were slightly overcompressed, but your engine is well run in and can take it. On my Cheetah 2.5, I start it by cranking the contrapiston in a half turn. then I open it a half turn and go fly. The exhaust is clear. One time I forgot to back it off, and could not tell anything different about how the engine ran, but it came down with fairly dark exhaust.

I started having carbon build up problems and broke some engines. I changed fuel brands and have not had any more problems. I had run the other fuel for years with good results.