Being Atheist as well as a "nerd" I would like to add something.
In regards to the "what if" stuff, yes, its entirely possible as the human brain is not fully understood, so the brain could percieve my blue as your purple. Science says otherwise, being that each frequency produces a certain color, however the absence of light is black, and the presence of all primary colors makes white. Again, though, people's brains percieve things differently, how do you know my white isnt your red?. It's impossible to tell, and may actually explain the horrid paint jobs on alot of cars.
If you dont accept the brain can see colors differently, then think of it this way: A dog will only ever see shades and mixes of yellow and blue, having dichromatic vision (meaning their primary colors are only yellow and blue), some color-blind people suffer from this as well, and some are even monochromatic (black and white). These people see this as normal, what I see as dark-ish gray, they see as blue. A "normal person"'s vision is trichromatic, or Red Green and Blue as primary colors. This will change our view on the world dramatically from one persons to the other's. Perception ALWAYS overrules science. Gravity tells us which direction is down, that is science, but in space there is no gravity, so what we percieve is down, is our down, and maybe someone elses left. Another example is before America was discovered, people thought the world was flat, we know this not to be true NOW, but according to their primitive science, it was true, and accepted. They also thought the sun revolved around the earth, again we know this not to be true now, but again, perception overrules science.
Also, as for the meaning of life: It's all about choices in my belief.
And finally, as for "42" being the meaning of life, it's not. It never was. It was the answer to life, the universe, and everything (IIRC), the meaning of life is an entirely different question. Plus half of 4 is 2, 4+2 is 6, half of 6 is 3, two and three makes 23 OMG! LOL