1920-30s Art Deco 0.55ct European Cut Diamond (E-F/VS1) Ring
Platinum, ~0.40ctw European Cut Side Diamonds (F-G/VS), (sold)

All three of these stones are basically perfect. The center stone is E/F color, which is colorless.  But it also has medium fluorescence, which means it fluoresces in UV light.  So in daylight it actually looks just slightly blue.