Because humans hear frequency in log scale, pink noise has more "even" distribution of amplitude to our ears.
Pink noise -> 100-200hz has the same power as 10k-20k ie each octave has equal power AFAIK.
White noise is defined as having equal energy per frequency; that is, a 10hz wide slice of spectrum centered on 100hz will have as much energy in it as a 10hz wide slice of spectrum centered on 1khz.
Pink noise has equal energy per octave; the slice of spectrum from 40hz-80hz has as much energy as the slice from 80hz-160hz and the slice from 1khz to 2khz.
Pink noise can be thought of as white noise with a very low-q (3dB per-octave, specifically) low-pass filter applied.
