I will try again to be clear.
This is based on the site's intention to present good quality images, taking account of the types and capabilities of cameras generally available to the average ship enthusiast at the time.
Subject to site standards generally, B&W images are perfectly acceptable where that was the original medium (usually roll-film) from the era before the mass adoption of colour photography. So far as I know, this has been unchanged site policy for a long time, if not since the beginning.
There can be no particular cut-off point, as the transitions from B&W to Colour, and from roll-film and/or slides to digi will have been different for each member. Members are expected to use common-sense and to refrain from trying to "game the system".
The expectation is that members will aim present the most natural results available from their resources. "Natural" here means generally "as perceived by natural eye" - it is nothing do with what is "pleasing to the eye". Nobody is picking on old B&W photos, it just happens to be the subject raised in the first place.