Dr. Link Check - Broken link checker with malware and parked domain detection
accessiBe - Making websites accessible to people with disabilities
BrokenLinkCheck - Free Broken Link Checker / Online Dead Link Checking Tool - find bad hyperlinks
Sim Daltonism - From the perspective of a color blind person, some colors are impossible to distinguish.
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Coblis - If you are not suffering from a color vision deficiency it is very hard to imagine how it looks...