This sometimes happens when you do colorwork. Yes, as GG suggests, you can cut the yarn and start the row with the purple color. However, if you decide to take out the row, the way to do this is to use the plum to cast off and at the same time carry the purple yarn across the cast off sts (fair isle
technique) and drop it at the body. That way it will be in place when you want to pick it up again for the next stripe.
I'm not sure about the marker either. Have you read the finishing directions? It may have to do with aligning the sleeves.