Xchox,
You do need to give yourself a slap, I'm afraid. The colour was not always green; there were red knobs on some. Put there because there wasn't room anywhere else... (Have you flown an Islander or Trislander? Space is, being polite to Mr Dore, at a premium).
However, you are right that some engines have been developed with automatic mixture control. The most MODERN aircraft I have flown with automatic mixture control was... The de Havilland Dove. It worked faultlessly in my experience and greatly reduced workload whilst maintaining economy.