Well Jan, I have a couple of chrome Leitz 5cm finders - a slightly 'beat-up' one on a B/C grade IIIa and a nice one on an A-grade IIIf.
The black III is the 'stealth' camera for candid/street work - often fitted with an Elmar or 3.5cm Summaron and a black lens hood, making it quite unobtrusive.
BTW, I saw your post about the Summarit - have you used it on a Barnack and if so, does it sit on the camera nicely? I have seen a very nice one for 500Euros but it may be a better deal for me to get a 'lux for my M4/M6.
Regards, Alan