I set out to reproduce a 2-color stranded cable swatch shown in Melissa Leapman's book of color knitting, and couldn't find any instructions about how to set up rows before the pattern began. The question was, whether to cast on in 2 colors? or to cast on in one color and then introduce the second color as you would in fair isle knitting?
The solution ultimately was to cast on in color A, then knit back across the row in A. That provided a base row.
Setup row(s): In the next row (right side),Based on how color appeared in the pattern CHART, I introduced the new color, B, just as you would in fair isle knitting. I knit 2 in A, knit 2 in B, knit 2 in A, knit 2 in B, etc. across the row, carrying the yarn across the back as you would in stranded knitting. Then I purled back using the matching color to purl the stitches (again carrying the yarn as in stranding).
Cable row: Then I was ready to begin the cable pattern using color B. This pattern calls for a C4 front (slip 4 to the front, knit 4 from the needle, then knit 4 from the cable needle). The fascinating complication here is that you slip 2 stitches in color a plus 2 stitches in color B. You must strand the yarn in the back when you pick up strand A to knit stitches in A, then strand B to knit stitches in B, first from the needle and then from the cable needle. Whew!
After this cable row was established, the pattern of Knit 2 (A), knit 2 (B), etc. was easy to read and execute. The next time the cable row came around, it was clear what to do.
If you've grasped the basics of cable stitches, and ALSO have done even a small project in stranded fair isle knitting, you can do this! You have to be comfortable with stranding on the back side. The result is beautiful.
I could not find a description of how this would work anywhere, and I couldn't conceptualize how to do a cable stitch with 2 different colors on the cable needle, so I just grabbed some needles and tried it out.
I hope this description is helpful if you are interested in trying this technique. Melissa Leapman's book has two examples. This was the 18-stitch cable pattern. I'm going on to the more complicated one next. Happy cabling in color!