I think I *may* have figured it out. The problem appears on the "K1, P1" rows. I have been holding the K1 color yarn (it's Color B) behind the needle and the P1 color yarn (Color C) in front of the needle. So when I do the purl stitch with color C, the strand that's carried to the next B stitch remains on the front (right) side of the blanket.
I think what I'll have to do is move the knit stitch color (Color B) working yarn to the front of my needles when I use the Color C yarn to actually MAKE the purl stitch. That way the B strand will be behind the purl stitch on the back side of the blanket, and it won't be covering up the "V" knit stitch on the front side of the blanket.
If anyone has done ribbing in the stranded method and you have a better, less awkward way of holding the two strands of yarn so that the B color strand doesn't rest on top of the front side of the blanket, I'd appreciate your tips.