A "color pair" is exactly two colors. There are ten color pairs in Magic: white-blue, white-black, blue-black, blue-red, black-red, black-green, red-green, red-white, green-white, and green-blue.
2019-05-03 • wotc
If the top ten cards of your library don't contain all ten color pairs, you choose as many cards as you can and put those cards into your hand.
2019-05-03 • wotc