When looking observations using the https://www.inaturalist.org/observations/identify, miniatures of these observation have an light tool which is very useful, but this tool is not available in observations inself (e.g. https://www.inaturalist.org/observations/00000000).
Are you asking about using the contrast tool in Identify? I asked about this a few weeks back and was informed that you can get to this really easily from observations by just clicking the “compare” button. I use it all the time now! Hopefully that helps (though it would save a click to have in on the observations page, but that might require adding a lot more “stuff” to the normal observation page that isn’t worth the work).
Yeah, as @cthawley says this is available if you click on Compare, so I don’t think we’ll add this to the standard page layout. I’ll close this request.