Sim Daltonism - From the perspective of a color blind person, some colors are impossible to distinguish.
Coloursimulations - Colour Simulations download page
Coblis - If you are not suffering from a color vision deficiency it is very hard to imagine how it looks...
Stark - Contrast check and color blindness simulator for Sketch.
Colorblind Web Page Filter - Enter a URL, and this tool will render it as someone with color blindness will see it.
Epilepsy Blocker - Block flashing GIFs that may cause an epileptic seizure