first, don't think about touching the original photo. scan it in at a high resolution and make a jpeg file for it. then, if you have photoshop access use it. you can use the paintbrush tool and set the opacity on like 20% and "paint" the color into the photo. it helps to make a black and white photo into a sepia tone before you add color. it just gives the photo a better look overall. if you don't know how to use photoshop and you want to do it by hand, then after you've scanned the image, print it out at whatever size you want on matte paper.