Yarn and needles: My rainbow is knitted with cotton yarn 8/4 and needles 2.0 mm but you can use any yarn and needles you like.
Estimated time: Half-an-hour.
How to knit
Knit yo's through the back loop.
CO 12 sts (purple).
Row 1: K4 * yo, K4 * (14 sts)
Row 2 : (blue) K2 * yo, K4 * K2 (17 sts)
Row 3 and every following odd row: Knit
Row 4: (green) *K4, yo * K5 (20 sts)
Row 6: (yellow) K2 * yo, K4 * K2 (25 sts)
Row 8: (orange) K5 * yo, K5 * (29 sts)
Row 10: (red) K4 * yo, K5 * K5 (32 sts)
Cast off and weave in ends.