It sounds a bit weird. When you enter edit, if the image is color, then that is correct behavior (and matches Preview). If the images are black and white outside of edit, then that also makes sense, if Photos is just using the embedded JPEG. Starting in color and going to BW and then going to color again is weird. That’s harder to explain unless the camera is being inconsistent about what thumbnails it’s writing (there are usually two or three thumbnails in the RAW).