Where one has an interest, they should google "prophoto rgb". There's plenty of available discussion, both high-level and quite technical. Some results from this google search will have interesting 2D and 3D diagrams of the various overlapping colorspaces. Others have examples of pixelation of blues of the sky as you edit in colorspaces with less coverage of these colors. Here's a link based on text and diagrams: https://luminous-landscape.com/understanding-prophoto-rgb/

If you step away from the highly technical 'why' of PhotoPro RGB and instead focus on the 'how', the advice becomes more practical. When you post-process your images, you have to choose which working space you’re in. This is the colorspace selection that your post-processing software then restricts you to use; no edit you make can lead to a color found outside your chosen working space. Therefore, as a general best practice for the RAW photographer, it is ideal that your working space is ProPhoto RGB when you edit your RAW images. That’s because RAW photos often contain colors outside of both sRGB and Adobe RGB color spaces, especially in high-saturation shadow regions. If you specify sRGB as your working space, you’ll automatically clip any colors that fall outside the sRGB range for every photo you edit. (Some software, like Lightroom, won’t even let you specify sRGB as your working space for this reason.)

BTW, colorspace is an attribute of the image editor and not the RAW image, so don't be concerned that ProPhoto RGB is not an option in the camera menu. If you shoot RAW and JPEG with the idea to use the JPEG SOOC as needed, use sRGB that creates your JPEGs ready to go and does no impact your RAW images, assuming you've configured your RAW editor to ProPhoto RGB. In the case of the JPEGs, your camera is the "image editor" outputting the files to the sRGB colorspace as appropriate for your web- and file-sharing needs.

It seems many UHHers use Adobe Camera RAW or Lightroom for their initial edits, then open the image in Photoshop for finishing. But, have they confirmed their export settings are creating images files in the ProPhoto RGB colorspace? If they review their setting and find 'no' for the ProPhoto RGB, they are likely using the sRGB or Adobe RGB working spaces, not realizing they are clipping colors when they go to PhotoShop or other tools to "finish" the image, aka 'discarding' lots of color data from the RAW file. To confirm and possibly correct: a) click on the blue link at the bottom of Camera RAW and change the images to ProPhoto, 16-bit. Or b) in Lightroom, go to Lightroom > External Editing > File Format = TIFF, Color Space ProPhoto, Bit Depth 16.

And finally, now that all your RAW / TIFF editing tools have been set to edit in ProPhoto RGB, you have an additional step when exporting JPEG images from Photoshop or LR to the web: converting them to sRGB. The absence of performing this additional step has become epidemic of late on UHH. See regular references to 'uncalibrated colorspace' and the drab appearance of colors of posted images. This final colorspace conversion step is rather easy to do with Edit > Convert to Profile > sRGB. Converting to sRGB for web images is essential; don’t let a ProPhoto image loose on the world where all your images look embarrassing drab when presented in browsers that expect sRGB.

Very good answer. I’ve always been a little confused about which color space to choose in my camera menu. After reading this thread, it doesn’t matter because I only shoot RAW. Does choosing Adobe RGB vs sRGB in camera affect the JPEG shown on the LCD?

Also, I edit in Lightroom, so I’m going to check that it is editing in ProPhoto. I know that I have Photoshop set to edit in ProPhoto color space. When I export as JPEG, they are exported with the sRGB colorspace.

Thanks for the detailed answer.

There's another reply later in this thread quoting Abode's documentation saying ProPhoto RGB is the default for the LR Classic Develop Module. I don't think you can find a place to change this. Changing the color space for LR applies to when files are created from the RAW, either via the Export module, printing, or creating files to pass to external editors.

Regarding the LCD display, that isn't the issue. I've never seen any reference to color space regarding how the camera's small onboard display uses the JPEG. The issue is how those JPEGs will be used away from the camera. If directly from the camera to an internet (or email) based usage without an editor, sRGB will give a more predictable result / display of those files wherever shared. But, if you still will edit the JPEGs and can convert to sRGB before sharing, using AdobeRGB provides a wider color space for editing those JPEGs.

One reason you should set the camera profile setting to sRGB for JPEGs is that it affects the appearance of the PREVIEW image stuffed inside of raw files. Your operating system (Mac Finder, Windows Explorer...) will display it more accurately.

Savvy pros know that the ONLY time to use Adobe RGB JPEGs is when a client requests it, or you KNOW that the entire downstream system is entirely geared up for that profile (i.e.; any monitor used for color adjustment is 99% or more capable of displaying the entire Adobe RGB color space, and the software is set to automatically apply the embedded or tagged profile).

It really doesn't matter what the profile setting is if you post-process raw files. A camera has a corresponding raw profile that exists either in your operating system or in your application software, or both. You can choose another profile when you export or save an image in an image file format such as TIFF, PSD, JPEG... (Raw isn't an image format... just a data format).