There are old time diamond merchants and jewelers who believe they can accurately tell anniversary rings size and quality with only a loupe, but we have found that they are often wildly off in their estimates.
Flawless GIA Certified Diamond are no more beautiful to the unaided human eye than a grade in the middle of the scale. Once again, extremely subtle differences in clarity are very important to determine rarity, but only affect beauty when in the very low end of the scale.
Extremely subtle color differences can be very important to determine rarity of a jewelry, but are never a critical factor in beauty.