Cylinder head cover discoloration

[Tezza_imp]

I noticed last time I had the cam cover off the engine that there was 4 small o ring type seals that appear to be part of the secondary air supply system. Only one of them had remained in the head and the other 3 had dropped down into the fins on the cylinder head. There doesn't appear to be a mention of them in the shop manual. If your cam cover has been removed at some stage they may have fallen out allowing exhaust gas to enter the area where the discoloration is.