Thank you for your response. The raw file looks different in PS vs. LR. LR is definitely darkening the image (and flattening it). I've never seen this before. Yes of course a RAW file in Mac Preview will look different than in PS or LR. I reset the develop settings and re-imported the images again. I made sure nothing weird was checked during the Import. So it looks like when they first get imported, they look fine (not dark). But as soon as I create a collection and click on one of the images (in the bottom scroll bar), they all start to darken one by one on their own. I've never seen such a discrepancy before between LR and Camera Raw. Why would anyone use LR to edit photos if it is not an accurate representation of what the photo actually looks like? What else can I do to fix this? Am I accidentally adjusting the exposure some how? I'm not doing anything different than I would normally do to look at the original photos I've taken.
LR and camera raw should look absolutely identical. If they don't, something else is going on such as some edits being applied in either one of those. It's also possible you are dealing with a bad monitor profile. The latter is very rare on Macs but can happen sometimes and is fixed by a recalibration.
>So it looks like when they first get imported, they look fine (not dark). But as soon as I create a collection and click on one of the images (in the bottom scroll bar), they all start to darken one by one on their own.
This is normal behavior. At first after import you see the embedded jpeg file that every raw file has. Those are replaced progressively by previews generated by Lightroom. My guess is indeed that there is some sort of preset or default applied. Can you go into Develop and post a screenshot of the develop settings. Alternatively, export the raw file as a dng and post that somewhere for us to check out. It will contain any Develop settings applied.
It is also possible that you are shooting using one of the dynamic range extending modes on your camera. Nikon, Canon and other manufacturers have these modes that automatically underexpose the raw file (so that you have a bit more highlight headroom) and contain a (proprietary) tag in the file that instructs the camera maker's software to compensate. This tag cannot be read by Lightroom or Camera raw. If this were the case, both Lightroom and Camera raw would look too dark.