A trio of a color and its two allies is known as a shard because of the shape that their triangle cuts out of the pentagon.
Grixis
Red Black Blue
Looking Out for Number One by Mark Rosewater
Bant
Blue White Green
Peace, Love, and Understanding by Mark Rosewater
Esper
Black Blue White
Striving for Perfection by Mark Rosewater
Esper Control 2016 by Shaheen Soorani
Naya
White Green Red
Searching Within by Mark Rosewater
There is one blue card and one black one but this deck is mainly designed to use green and red mana to cast white cards for free.
Jund
Green Red Black
Following Your Heart by Mark Rosewater
We 5-0'd with our first league of this on stream today. Some tweaks to be made, but was a delight :) Goryo's Vengevines! pic.twitter.com/WeSKx8ulVa
— Autumn Burchett (@AutumnLilyMTG) August 25, 2017