Dan,
I have a bog standard Chipmunk T10 sitting in the hangar, albe it ex-Navy, and it has a four prong spring thing on the Left side beneath the RPM gauge for the stopwatch. The back seat does not have it, but there is a Normal/Mute switch in that position so it may have been changed at some time.
As for the color, they were all painted in zinc chromate rather than the cockpit green that the Tiger, Magister, Anson etc. were. Zinc chromate varies in shade from a Yellowie Green to a very Dark Green as can be seen inside mine after various repairs/additions were made. Then the cockpit area from the back of the back seat to the firewall were over sprayed in Matt Black.
Speedbird 48