When was the pink brick released?
There are two shades of light-pink in LEGO's history that were included in official sets. (Please note that there are other, rare shades of pink that never made it into mass production but were used as test colors or for special projects.) The older light-pink is simply called "pink" in the BrickLink Color Guide, and also often referred to as "Paradisa Pink", as it was in the LEGO Paradisa line where the color was most prominent. It is a softer, lighter shade, and was produced between 1991-2006.

The current light-pink is referred to as "bright-pink" in the BrickLink Color Guide. It was introduced in 2003 and is produced to this day. It is a much brighter and bolder color. 

Besides these two light-pink colors there are also darker pinks: the older medium-dark-pink (1992-1996), the current dark-pink (1994-), and also current magenta (2000-). 

You can find detailed information on them in the BrickLink Color Guide, and you can see sample parts in each color here: BrickLink Color Guide with Images.