HyperColor is a brand of clothing popular during the late
1980's and early
1990's. I believe the line included
t-shirts and
socks. The garments respond to temperature differences by changing colors. For example, a green shirt might turn purple when you place your hand on it (if you're not already wearing it.)
The following explanation of the science behindHyperColor clothing appears on the Department of Energy's "Ask a Scientist" webpage. It is authored by Gerald Bokowy.
URL: newton.dep.anl.gov/newton/askasci/1993/chem/chem009.htm
Hyper color shirts are discussed in "chem matters" October 1992 issue. There are actually two dyes in hypercolor shirts. A basal color dye that is always present, and another that is colorless when cold and blue gray when warm. Each hyper color capsule is 15 to 35 microns and contains several extractable dyes. If you want more the article's explanation is extensive but written for high school chem students.