c/o 230 sts in long tail - k1, p1.
~35 rows in seed stitch in gray.
~reserving 20 stitches on each side in seed stitch, knit 14 rows stockinette in gray.
~Switch to 1st CC and knit 35 rows in stockinette, keeping 20 seed stitch stitches on either side.
~Every 35 rows switch colors and finish the far end the same way you began with 14 rows stockinette and 35 rows seed stitch.

A thought: next time I make this blanket - if there is a next time, this was #3 - I think I will alternate 35 rows knit, 35 rows purl, switching with each new color so that the blanket is completely identical on both sides and there is no back or front.