Coblis - If you are not suffering from a color vision deficiency it is very hard to imagine how it looks...
Colorblind Web Page Filter - Enter a URL, and this tool will render it as someone with color blindness will see it.
Color Oracle - Color Oracle is a colorblindness simulator for Window, Mac and Linux.
Stark - Contrast check and color blindness simulator for Sketch.
RGBlind - Browser extension to simulate color blindness.
Color.review - Colors that look and work great for everyone.