You can format the color and underlining in the Format Cells dialog box. To make it easier the next time, highlight the changed cell and set up a style (97-2003) or cell style (2007-10).
Similarly to Excel®, it’s a simple format font exercise to change the color and underline. In both versions you can save a new style to make the change more quickly next time. Search for help on “create a new style” (97-2002) or create a new quick style (2007-10).
PowerPoint® is a little stubborn. In 2007-10 you can adjust Theme colors. In 97-2003, you can adjust Color Schemes in the Slide Design task pane. However, the underline isn’t going anywhere! A workaround is to draw a rectangle over the plain text that would have been your hyperlink. Change the fill to No Fill and the line to No Line. Right click on the new “invisible” rectangle and insert the hyperlink.