The Spectrum Sweater © 2009 Kaleidocherry

Following is the detailed information (with commentary). For a printable PDF file of the pattern (sans commentary) click here.
28” length, gauge 5.25 stitches and 7 rows on 4.25mm needles. Stockinette stitch throughout.
Yarn: Lunatic Fringe Yarns’ Tubular Spectrum in 10/2 mercerized cotton (all colors) plus black, and UKI 10/2 mercerized cotton in "Yale Blue." The Color Gamp Kit from Lunatic Fringe ($72) should provide enough yarn to finish the project. I like this yarn and plan to work with any leftovers in the future, so I simply ordered three Color Gamp Kits. This means I don't need to wind off anything. You will be working with three strands of yarn at once. Sometimes all three strands will be the same color. So if you only order one kit, you will need to wind off either one more ball (and work from both the center and the outside of the ball, plus the remainder of the cone, when you need three matching strands) or two balls (and work from each ball, plus the remainder of the cone, when you need the three matching strands). See here for a picture of the Tubular Spectrum.

What we are doing with this project is making an even, gentle color progression, starting with the dark purples at the bottom and working up to purple blue at the collar. (Note: my prototype is different from the pattern. I rewrote the pattern after working most of the sweater, to eliminate some of the issues I had.) By using three fine strands, we can swap out a strand every few rows and make the color progression more subtle. You could, of course, work a sharper contrast by always using three strands that match: working 9 rows of each color, and having a clear line delineating each color change.
Why do we need the UKI yarn? Because the Tubular Spectrum doesn't have a good true cobalt in it, which means that their color progression goes from a turquoise color to a purple. Yale Blue from UKI makes the transition work.
Note that the schematic finishes at row 196, but I wrote the pattern for 2 more rows to give a full set of the color progression and to add one row for seaming.
With 3 strands of black, cast on 139 stitches. Work in stockinette for 8 rows.
Row 9: remove one strand of black and add in one strand of 5 Purple. Work in stockinette for 3 rows.
Row 12: remove one strand of black and add in one strand of 5 Purple. Work in stockinette for 3 rows.
Row 15: remove the final strand of black and add in the final strand of 5 Purple. Work in stockinette 3 rows.
Continue working in stockinette, in the color progression (see here for a detailed breakdown by row) for the rest of the sweater.
Back Bodice and
Sleeves
Row 132: Cast on 10 stitches at the beginning of each of the next 6 rows. What we are doing here is extending the shoulder drop to create an integrated t-shirt sleeve, so that the sleeve stripes will not end up at right angles to the body of the garment. Work even until row 198. Bind off all stitches.
Repeat body instructions for front piece, then
Front Bodice and
Sleeves
Row 132: Cast on 10 stitches at the beginning of each of the next 6 rows. Work until row 175, then
Begin Neck Shaping
Work to center 24 stitches, attach another ball of yarn, bind off center 24 sts, complete row. Work both sides at once.
Bind off 2 stitches at each neck edge 2 x.
Dec 1 stitch at each neck edge, every other row 5x.
Continue until row 198. Bind off all stitches.
Seam shoulders using 3 strands of 10 Blue Purple. Seam underarms using 10 Green.
Cuffs
With WS facing, using 3 strands of black, pick up stitches around the sleeve opening. Turn to RS facing and work 10 rounds in stockinette. Bind off loosely, leaving a long tail. Fold the curled part back over the color section and use the long tail to secure the bound-off edge to the right side of the sleeve.
Neckline
Finish the neckline in the same way. Weave in all ends.