Well I thought of a Purple Hammer - Does that mean I am 50% normal?
When you force the brain to do things quickly it relies on instinct.
I would imagine that a hammer is one of the first tools that we learn about - if you were to conduct this test in a society that hammers did not exist in - You would never get hammer as a response.
As far as colors go - I would imagine that you would normally get either red, blue, yellow, black or white.
I would say that is because they are the most basic colors in our comprehension ( I know that black and white are not primary colors - but they are basic).