The collection at www.rskey.org shows two types of 32SII. The older type (brown bezel, yellow/blue labels) is dated 1991-1999. The newer type (silver bezel, teal/lavender labels) is dated 1999-2002.
If rskey is correct, then the 32SII was redesigned in 1999. This is consistent with my old-style 32SII, which is dated mid-1998. The redesign may have coincided with a packaging change in the US, from cardboard boxes to clear blister packs.
The 20S was apparently redesigned at about this time as well. The 20S underwent the same change in label colors (though the bezel stayed black). I have a 20S with teal/lavender labels dated mid-2001.
Curiously, the 20S owner's manual apparently did not get updated to reflect the new color scheme. The front cover of the manual that came with my teal/lavender 20S shows a model with yellow/blue labels, and the text inside explicitly refers to the yellow/blue labels. The manual is Edition 6, dated 11/94.
I can compare the two 20S color schemes by placing the calculator and the manual side by side. The yellow/blue scheme appears to be much superior.