What’s it for?
Some kind of help on color theory?
Anybody have any pointers?
Nice site. 
It’s for finding complementary colors for web design. Nice touch that it even provides the hex notation.
Pantone is the brand name for a company that produces color swatches . You can still buy them in art stores . They come with hundreds of pages of color variations and was used by graphic artists because they developed a formula for aspects of color based on chromatic scales and hues and provided specific chemical keys for those colors to the printing industry .
Looks like the site provides you with complimentary colors based on hue/chroma (that’s why you see sets of two?)
sorry, but this doesn’t belong in this forum.