Oh, how neat is this? The blue shows water vapor, or as the caption states:
Aquavision False color image from GOES-E Satellite taken on September 2, 2010 0000 UTC.
RGB[IR4, IR2, WV] composite. In the image Category 4 Hurricane Earl moves northwest towards a frontal system draped across the North America that had deformed in to a straight wall. The blue water vapor outflow of Hurricane Earl swoops down to the SW, while the overall flow of the frontal system moves water vapor from the tropical system near Baha California up towards Greenland.
Image credits: EUMETSAT / NEODASS / DSRS / NASA / processing by Mike Malaksa