The idea is pretty basic, when working on a project people tend to make snap decisions and then stick to them. This system helps one to take six new views to older ideas:

• Questions (White) - considering purely what information is available, what are the facts?
• Emotions (Red) - instinctive gut reaction or statements of emotional feeling (but not any justification)
• Bad points judgment (Black) - logic applied to identifying flaws or barriers, seeking mismatch
• Good points judgment (Yellow) - logic applied to identifying benefits, seeking harmony
• Creativity (Green) - statements of provocation and investigation, seeing where a thought goes
• Thinking (Blue) - thinking about thinking

Six Thinking Hats from Wikipedia

Article from Lifehacker