There's more than one way to get at this. Here's the way I think will be fastest for your situation. Highlight / select all the text you want continuously underlined. In the Home ribbon menu, click the symbol for underline and make sure it is all underlined. Then click the little down arrow beside the symbol for underline. From the drop down menu that appears, select "underline color" at the bottom. From the color selector that appears, pick your color.