I have many of the issues and the publisher has definitely improved as time moved on -- e.g. their earlier issues weren't very informative as it seemed to have redundant photos seen elsewhere.
I'd say that the more recent issues (circa #50 and beyond) have better photo coverage.
As for the color plates, they are interesting and can be a source of inspiration but that's it for me. We assume the artist is painting from a known picture (almost 100% likelihood of b/w) but it's only his interpretation. I never rely on published color plates. Sheer speculation in my opinion.
And yes, the color plates include markings.