What is white, pink, blue "brown" noise?

What is noise?
noise is random frequencies at random sound pressure levels or random voltage spikes populating a given spectrum.
you are all familiar with the static on your tv on channel (pick a blank channel) it is like light, white noise is like white light it has all of the frequencies that we can hear (even the ones that we cant hear).
a calibrated white noise is random frequencies in a given frequency range that all have the same loudness. the graph would look flat across the board.

Your static on your tv is not a calibrated white noise, it is a random white noise and cannot be used for calibration because it is inherently colored (this color can be graphed)

so what is pink noise or red noise?
is there really such a thing as brown noise?
how about blue noise?

well yes, you can have any color of noise just like you can have any color of light.
by adding more "volume to higher frequencies, you can generate a blue colored noise this type of "hiss" would sound like it has more treble added to it.
some scientific research would use blue noise to calibrate instruments, also, speaker manufactures would use different colored noise to calibrate their loudspeaker cabinets.

here is a graph of blue noise

So what is all of the Hoopla about pink noise?

well pink noise is special
when you have a sound system you need to calibrate it to the human ear.
the human ear it turns out has a frequency response just like a microphone (see frequency response).

if you were to graph the frequency response of a healthy human ear, you would get something like this:

see how the frequency response dips in the higher frequency range and also note how there is a peak in the lower end of the spectrum?
in pink noise, also called "1/f noise" is a signal or process with a frequency spectrum such that the power spectral density is proportional to the reciprocal of the frequency. WHA???

basically, pink noise has more energy on the frequencies added to the low end to compensate for the humans frequency response to "flatten it out"

for more in depth information on noise, look here
http://en.wikipedia.org/wiki/Noise_%28physics%29