A couple of weeks ago I was giving a training and somebody made the remark that if something has the color red it is critical. The logic she used was parallel to the traffic lights but there is a problem with this. It starts with the idea that everybody can see colors and this is not the case.A good friend of mine is color blind for red and green and that is how I became aware of the issue.
When we are talking about a traffic light what color is lit actually, since we agreed upon the fact that the colors are in an order and it is thus actually the order of the light that matters and not the color. This is why color blind people are able to drive.
When we are talking about incident response this becomes an whole other issue since the color tag of an incident is pointless to a color blind person. If my friend would have a look at a dashboard tagging one incident red and another one green they would both be grey-ish. This means he has a 50% chance of starting to work on the incident with the least priority.
The solution is actually pretty simple, you use a defcon-type scale where 1 means it is your number one priority and the lower on the scale the incident is rated the less attention it will get. The classification of your incidents will influence greatly the value it gets on this scale.