Are you wanting to knit with two colors, such as stripes, or just add a different color fringe? If you knit flat and want two use two colors you can just change the color at the end of a row and have stripes; other ways of knitting with colors are more complicated. If you want to add fringe, that's easily done. Let us know more and someone can surely help you figure it out.
I should never overestimate my basic arithmetic skills.