I suppose the title should really be "Three Shades of White and Shadow Blue", but here it goes, anyway...
At the tea shop a couple of weeks ago, while drinking some of Taiwan's best oolong, Prof Ahn poured our cups full then, uncharacteristically, gathered them together and asked, "Which one has the nicest colour?"
Gazing into the cups, I was surprised to see the distinct difference in tea colours, even though they'd all just come from the same pot and into Qing Dynasty cups. I observed my tea had a nice teal tint, Prof Ahn's tea was very similar but more green, and his employee's tea was ocher coloured.
He explained that the difference, as I'd already guessed, was in the shade of the cup. There are four different shades of white tea cups; milk white, snow white, ivory white, and "shadow blue". Milk white is pure white, snow white has a blue tint, and ivory white has a yellow tint. Prof Ahn's cup is celadon with a crackled glazed, darkly stained from years of use, but he referred to its colour as "geurimja-paranseak" (shadow-blue). Mine was a porcelain "Double Happiness" cup with a blue "snow-white" slightly blue tint, and the third was also porcelain but with an "ivory-white" tint. He added hat snow-white cups are best for admiring tea.
At home, I gathered a few of my cups picked one of each shade and experimented by comparing how they affected the colour of
Bai Mu Dan (White Peony). The difference was subtler than with the brightly coloured oolong at Kkikdageo, but still noticeable. In the above image, starting with the top-left and going clockwise is snow-white, milk-white, ivory-white, and the closest cup I had to shadow-blue. You can see, the milk and ivory whites are very similar, as are the snow-white and shadow-blue.
Why does this matter? Well, depending on who you are, it may not matter at all, but much like with wine tasting, there are steps in appreciating tea, and admiring the colour is one of them.