Do we switch colors for the purled side seam stitches after the markers since the dominant color has changed?

I just finished Clue 4. I am loving this project! Out of an abundance of caution, I ordered some more of Color C, especially because I am also using it as my Color D.

I am loving this knitalong. The sweater looks amazing and the pattern is so easy to follow. Can't wait to see clue 5.

I just finished Clue 3 this morning. Now I need to figure out whether I should go with the straight fit or the shaped waist in Clue 4.

I have a question about the steek stitches in the cardigan version. In the instructions for the 30 rows for Clue 2, it says to alternate Colors A and C. But should this be continued in the rows when only Color B or when only both Colors B and C are in the row? I guess I am wondering whether the A/C pattern in the steek stitches will be important for the button bands.