All the other weather icons seem to be present, but when the weather is clear or sunny, the icon reverts to an ugly yellow sun instead of the lovely mono icons. Why is this icon missing?
Quick and dirty workaround for this Weather Indicator bug (will modify an icon file that is part of a package):
Download the monochrome icon from the main bug report:
Backup original colorful icon from package:
cp /usr/share/icons/Humanity-Dark/status/48/weather-clear.svg /usr/share/icons/Humanity-Dark/status/48/weather-clear.svg.backup
Replace colorful icon with monochrome icon:
mv weather-clear-light.svg /usr/share/icons/Humanity-Dark/status/48/weather-clear.svg
Restart Weather Indicator to enjoy monochrome icon.
This is a regression introduced in Natty. The developers are still deciding which is the best fix for this. See bug #748861