Cast on 5 sts.

Simple triangle construction with 2 border sts on each side in garter, 1 yo between border sts and stockinette body and a central ktbl st with 1 yo on each side.

Changing yarn colour every eighth row plus some 2-row changes in between (see pictures).
Working the border st at the beginning of each RS row with both colours to avoid sewing in dozens of yarn ends.