Comment by 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!”