The 25c low-value Beneficial Insect stamp (Scott 2238) has been reprinted.
The original printing (Oct 12, 2007) has a blue-green tinged gum.
In early December 2012, the stamp appeared with the transparent colourless ("white") gum.
This image shows it a bit. The white gum variety, shown at left under the blue-green stamps, should be 'whiter'.

This series is turning out to be very interesting (see:
http://www.adminware.ca/checklist/chk_insect.htm)