cast on 100 sts with US 4. 2x2 ribbing.

3 rows grey 1
1 row navy
3 rows blue 1
1 row navy
3 rows grey 1
1 row navy
3 rows blue 2
1 row navy
3 rows grey 2
1 row navy
3 rows blue 2

and so on, and so forth.

switch to US 6 after ribbing, continue in striping pattern.

setup round for decreases: decrease four stitches evenly across one round. after that alternate 1 row plain knitting with one round of decreases (8 decreases per row).