The
amplitude distribution of
white noise is flat
Hz-wise - the frequency bands 25-30 Hz and 1025-1030 Hz contain the same
energy. Pink noise, on the other hand, is flat
octave-wise, and since the relation between octave and frequency is
logarithmic, pink noise will
attenuate at higher frequencies - 500-1000 Hz will contain the same amount of energy as 250-500 Hz does, thus leaving the energy-per-Hz ratio for the 500-1000 Hz
band at .5 compared to the 250-500 Hz band.
The name comes from the color of pink noise in the visible electromagnetic spectrum - the lower frequencies (reds) dominate.
Pink noise is often preferred to white noise when testing audio equipment, since the spectral distribution is closer to actual music.