This increase is used in my pattern Madrigal, but would also be useful for other stranded knitting where it fits in. I’ve called it AC-increase because the pattern colors in the Madrigal pattern are A, B, C, and D, and the colors A and C are used for the increase round. A is navy blue and C is pink, and C is the dominant yarn.
The AC-increase is worked by knitting two stitches in one, first a stitch with the non-dominant color A (picture 1), then with the dominant color C (picture 2).
Here, AC-increases have been worked in the last two stitches:
When the stitches are reached on the next round, simply work them one at a time as you reach them. The increase is quite well hidden – the arrows in the picture below point to a couple of AC-increases
