This is the latest chart for Pearsall Silks I have found, December 2011. It does not originate directly from Pearsall, but from a material supplier the
Pearsall's Gossamer / Langley Superfine Silk
Pearsall's Gossamer Silk Thread has been in use since 1795 - probably first named as a tying thread in Thomas Evan Pritt's book - "North Country Flies" in 1885. This is a quote from their web-page.
“Since 2002, Langley Threads of Cardiff, Wales have been dying the gossamer shades for Pearsall’s; I have been working with John & Carol at Langley to re-introduce many of the shades that have been discontinued for as long as 35 years.”
This is the web address for the Flytying Boutique :-