Inspecting a file for color pixels probably could be done, but it would be very difficult. It's beyond my knowledge.
An easier, but not 100% reliable, method would be to look at the metadata. This is not reliable because you have to count on prior software processes to correctly write color metadata and that doesn't always happen. Having said that, if your files have been processed that same way, then the metadata should be consistent, at least consistent enough to locate most of the color images. You could then manually test the remainder.
Here's one easy clue: your sample images are RGB
You can also see this in the Filter panel, but it shows the difficulty in relying on metadata.
rocks is sRGB
water is untagged (color images can also be untagged, unfortunately)
Have a look at the greyscale version of water.jpg and see what the Filter and File Properties say. Your file metadata might be consistent enough to identify the not-really-b&w images just using standard Bridge tools.
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