Thanks, David, no transparency anywhere that I can see. All 3 look exactly the same in Photoshop. But one must be different somehow. I solved it, I think, by saving the offending image as a Photoshop PDF, and converting it to sRGB — then placing it in the InDesign document. I suspected it might have something to do with a color profile, but could not find any different profile applied in the original Photoshop files. My PDF “fix” worked! All 3 now look the same, as they should!