Thanks for your inputs raymoh, sboerner, because that was really puzzling me. I agree that such differences would not be visible, unless you are a mantis shrimp. But I can still think of a situation or two, when that could play a role.
I think you may well be right sboerner. I never thought that RGB values could be a subject to rounding though. The more you know.
I need to try other input formats indeed, although I'm not sure if that will work or the same would take place. I'd have to make sure if other formats are available though, because I use Wikipedia "shades of..." pages and didn't notice what other formats do they cover.