[watwut]

Pro-tip: there are browser extensions able to simulate various kinds of color blindness.

That is better then a random friend, because a.) there are various kinds of colorblindness b.) you wont ask the random friend to work for your company for free.

[cwillu]

On the other hand, the random friend generally has a great deal of experience with what interventions help and don't help.

A filter shader generally won't tell you that substituting white for green in a red/green indicator is a great option, or that a colour that they can “see” is still ambiguous when you have to describe it: “I'm clicking the purple button, but it's not doing anything” “Purple? There's no purple in the app!”