Since version 1.40 pdfTeX supports several color stacks; the package uses a separate colour stack for control of transparency (which is not, of course, a colour).
The package is part of the oberdiek bundle.
The author is Heiko Oberdiek. The package is Copyright © 2007 Heiko Oberdiek.
License: lppl1.3 Version: 1.0 Catalogued: 2012-08-23