Many labs, on their websites, don’t mention your Photoshop settings at all; but some give very specific advice about how your Color Settings should look. These guidelines vary a little from lab to lab, but generally these two are common:

They tell you your RGB working space should be sRGB, and the Policy is for all images to be converted to that space.

I completely understand why labs do this. They know what colour space is correct for their printer/paper setup, and as long as all their customers send their files in this colour space, they (the lab) have a completely stress-free life. Files come in, prints go out. The prints that go out are a perfect match for the files that came in. The lab is happy. And almost all the time the customers are happy too.

But despite all that, I do NOT recommend changing your Color Settings this way. They must remain on “North America General Purpose 2” at all times:

Why? Because “Convert to Working RGB” is a blunt instrument. If you open a file with a different colour space, it brutally changes it to the working space without any consideration for gamut or clipping. It doesn’t give you an opportunity to check whether there are colours too vivid for the working space. If too-vivid colours are converted without warning, clipping and loss of detail occurs.

The NAGP2 setting leaves all images in the colour space they were given. Then you can decide whether to convert them, and if so, soft-proof beforehand to prevent clipping.

For most of you, most of the time, this issue will rarely arise. You will be editing your own raw photos which you have already processed in sRGB. But sadly it’s very common for template, texture or overlay files (such as you might purchase from Etsy or wherever) to be in Adobe RGB. If you encounter this, you must wisely check them before converting.