Originally Posted by Artificial-I
Normally this is due to a few situations including fuel that uses bad quality castors and oils can cause this.
What fuel you running?
All fuels who use Castor oils will leave a tan/brownish residue due to the fact you're burning castor oil insted of synthetic oils who burn at lower temps and protect much less your engines.
Is not bad at all to have tarnish on your combustion chamber/sleeve/piston top. In fact you can see how well or bad is burning looking at those burning marks.
The soot could be cause by an improper carb tunning (generally too rich) and don't generating enough temp to burn the soot.