Hi Sue, and welcome! The best way to carry yarn up the side of the scarf is to leave the ball attached. Then pick up and knit with the new color. After two rows, bring the old color up and twist it with the new color, then keep knitting with the new color, twisting at the end with the old color every two rows. Then when you're ready to knit with the old color again, it will be there, ready and waiting.