Take away the color treatment and the underline will let visitors with color blindness know that it is a link.
Image maps also pose a problem for color blind users.
A good practice may be to create the site in grey scale colors because elements should never rely solely on color. Images, links, buttons, and other similar elements should be enhanced with an image, shape, positioning or text.
For example, a link should be highlighted by color as well as underlined.
Any links or buttons on the site that are essential in aiding the user to accomplish their tasks would fall high on the essential list.
The standard rule: any content that the user may look at for more than two seconds should be made clearly visible and have a high contrast ratio.
Those with color-blindness are not the only visually impaired users and adding all visually impaired greatly increases this population.
For this group, you run the risk of having a Web site that the text is barely legible and the images unrecognizable.Other issues to consider are the contrast between colors and the background.People with color blindness are less sensitive to colors on either end of the spectrum.The challenge of designing for color blindness is because it is hard to determine what color blind users see and how that is different from what the average user sees.
And the difference between the different types of color blindness just adds an additional layer of complexity.
Image maps have clickable areas that are often delineated by color.