If your images come out of the camera named something like this:
What does that underscore mean? Why not “IMG”instead of “_MG”?
It’s Canon’s way of telling you that you have set your colour space to AdobeRGB instead if sRGB. This colour space setting determines how the conversion from RAW to JPG is done. If you are shooting JPG, the camera produces images in that space; if you shoot RAW, it tells the program at the other end you would prefer that colour space when eventually making JPGs.
And sRGB is the right setting in almost all cases, hence the warning if you use AdobeRGB. Although AdobeRGB has more colours, it needs software to show it properly; most software and most screens show sRGB much better; AdobeRGB looks dull on these devices.
ANyway now you know what that underscore means.