This project begins with the sleeves.  I find that if I knit the sleeves of a sweater first, the rest of the sweater zips along much faster.  I realize that this is a total mind game, but that doesn't stop me!  So here we go with the sleeves:

 

SLEEVES (MAKE TWO)

With Color 2 and short circular needles or dpn, CO 32(38) stitches.  Join into a round, taking care not to twist stitches. Place a marker at the beginning of the round.
Round 1: *K1, p1, repeat from * to end of round.
Continue k1, p1 ribbing until sleeve measures 3 inches, about 18 rounds.

STRIPES IN THE ROUND
Now we introduce Color 1.  Leave a 6-inch long tail of Color 1, just as if you were starting a new ball of yarn.  Do not break yarn for Color 2.
Round 1 (with Color 1): Knit.
Round 2 (with Color 2): Knit.
Repeat these rounds 2(3) times more (for a total of 6 (8) rounds).

INCREASE ROUND
Next round:  Kf&b, k to 2 stitches before end of round, kf&b, knit last stitch.     

Continue to work in this manner, increasing one stitch on either side of the marker every 6(8) rounds 9(8) times more, until there are 50(54) stitches on the needle.  

Continue knitting (no more increases) until the sleeve is 17(20) inches long.  

Here's what it looks like in progress, resting color on the left and active color on the right as you knit it.

Because you are knitting stripes that are only one row tall, there is a very slight, almost negligible, jog in the color from one row to the next.  The jog becomes more visible with wider stripes of two or more rows.  If you want to eliminate this interruption, you can read a good summary of Meg Swansen's Jogless Jog on NonaKnits.

As you twist the yarn the same way at the beginning of each round, it makes a nice neat detail on the inside of the knitting:

Final Round (with Color 1):  Knit to end of round, remove marker, K 3(4).

Place previous 6(8) stitches on a holder. Break yarn, leaving a tail.

Set aside the first sleeve and make a second one the same as the first.