Intarsia patterns can be worked in the round on the leg portion of the sock.
You will use a yarn over and a decrease at the end/beginning of the round to reverse directions to implement your Intarsia pattern. For all but the 2 circulars method, the beginning of the round is on the first stitch of one needle and the end of the round is on the last stitch of another needle.
4 dpns
Beginning of Round: 1st stitch on N1.
End of Round: last stitch on N3.
5 dpns
Beginning of Round: 1st stitch on N1.
End of Round: last stitch on N4.
This is also the center of the back of the leg.
2 circulars
The center stitch of N1.
Divide the stitches on N1 in half and place a marker. Consider the stitch before the marker as the end of the round, and the stitch after the marker as the beginning of the round. (center of the back of the leg)
Round 1: Knit side. At beginning of round, yarn over, knit to the end of the round adding your Intarsia Motif colors. When you reach the end of the round k the last stitch tog with the yarn over.
Round 2: Turn. You will now purl. YO to put the yarn in the correct position. Purl the round working your intarsia motif. At the end of the round purl the last stitch together with the YO.
YO, Turn, and Knit the next round.
The sock is still in a circle. The right side is facing you, but when you YO and turn you are purling on the inside.
I have seen many socks with lovely Intarsia in the leg section, but the leg is knit with two needles and then seamed. The seam is always visible and often bulky. With this method, there is still a seam line, but there is no bulk to it.