Plain Language Recommendations
Colour alone must not be used to distinguish links from surrounding text unless the luminance contrast between the link and the surrounding text is at least 3:1 and an additional differentiation (e.g., it becomes underlined) is provided when the link is hovered over or receives focus.
WCAG 2.0 Recommendations
Guideline 1.4: Distinguishable
Make it easier for users to see and hear content including separating foreground from background.