What is a good way to ensure that a web-app user does not make a potentially dangerous choice or recognizes that an undo is necessary?

Scenario (anonymized):

  • Red pills must not be sent to color-blind customers since they could mix them up with the regular green pills and die.
  • The color-blindness attribute of a customer must not be stored in the customer database.
  • The web-app user can ask the customer about their color-blindness while placing the order (think call center).
  • Color-blindness probability in the relevant customer population is at most 1%.
  • Update: Ordering red pills is a rare event.

Current proposal:

I am thinking of a two-step page where the user is reminded of color-blindness issue in a help text below the Yes, mail pills option. After selecting Yes, mail pills and placing the order, there is still a possibility to undo the action. Since color-blindness probability is so low I am afraid that users will still habituate to click Yes, mail pills.

First step of confirmation page. After pressing "Yes, mail pills", the second step is reached, allowing undo.


  • Is this the least bad design for confirming/avoiding/undoing a potentially but very rare fatal action in a web app?
  • Apart from storing color-blindness in the customer database (not allowed) can I do anything else to avoid the dangerous action?

2 Answers 2


I would require a checkbox that confirms that they have checked that the person is not color blind. That way, the "Yes, mail pills" button does not even become active until they have verified. That makes the second step unnecessary. This seems like the simplest option to me.

  • That was my initial thought, too, but isn't that a variation of a second confirm and frowned upon since in 99% of the cases the check box just slows the user down in placing the order? Wouldn't I still need an undo in case the user clicked the checkbox out of habit?
    – AHalvar
    Feb 26, 2017 at 8:02
  • That's true. Taking into consideration the percentage that the colorblindness is relevant, perhaps a better option would be an unobtrusive undo option. I was thinking that you wanted to force the user to stop and think, but if not, then an undo option that doesn't disrupt the flow of the average user and doesn't require clickthrough to escape. Like Gmail's undo option after you delete an email. Feb 27, 2017 at 2:48

Actually, I think that the message is not highlighted enough. Some people might not even read the small letters under the button. I would use something like: "My customer is color-blind" vs "My customer is not color-blind".

I really like the undo option. I would also give a message of what kind of pills the user has ordered. What about a warning sign as well?

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