...and then he was like...

Alex responded with this. He was walking right into my trap.

You would use the naked eye of anybody who has fully functional color vision, in conditions of appropriate [a sufficient source of white light] but not excessive lighting, from a distance such that the shirt is visible, without any objects [including opaque gasses] obscuring the view, and such that the observer is fully comfortable etc [and I reserve the right to add a million little other details in as necessary]. I don’t see what you are getting at with the request for an extremely detailed listing of the process.