The following is an excerpt from John Culvenor and Dennis Else Engineering Creative Design, 1995)
White Hat on the Hats
There are six metaphorical hats and the thinker can put on or take off one of these hats to indicate the type of thinking being used. This putting on and taking off is essential. The hats must never be used to categorize individuals, even though their behaviour may seem to invite this. When done in group, everybody wear the same hat at the same time.
White Hat thinking
This covers facts, figures, information needs and gaps. "I think we need some white hat thinking at this point…" means Let’s drop the arguments and proposals, and look at the data base."
Red Hat thinking
This covers intuition, feelings and emotions. The red hat allows the thinker to put forward an intuition without any need to justify it. "Putting on my red hat, I think this is a terrible proposal." Usually feelings and intuition can only be introduced into a discussion if they are supported by logic. Usually the feeling is genuine but the logic is spurious. The red hat gives full permission to a thinker to put forward his or her feelings on the subject at the moment.
Black Hat thinking
This is the hat of judgment and caution. It is a most valuable hat. It is not in any sense an inferior or negative hat. The black hat is used to point out why a suggestion does not fit the facts, the available experience, the system in use, or the policy that is being followed. The black hat must always be logical.
Yellow Hat thinking
This is the logical positive. Why something will work and why it will offer benefits. It can be used in looking forward to the results of some proposed action, but can also be used to find something of value in what has already happened.
Green Hat thinking
This is the hat of creativity, alternatives, proposals, what is interesting, provocations and changes.
Blue Hat thinking
This is the overview or process control hat. It looks not at the subject itself but at the ‘thinking’ about the subject. "Putting on my blue hat, I feel we should do some more green hat thinking at this point." In technical terms, the blue hat is concerned with meta-cognition.