Don't you hate having to look outside whenever you want to know the weather? Talk about a hassle!
Freeware tool AeroWeather puts Windows Aero (the graphical interface introduced with Vista) to practical use, retrieving the temperature or current weather conditions for your location and changing the color accordingly.
So, for example, if it's particularly cold outside, AeroWeather will fade your UI to purple. When it gets warmer, look for redder colors.
Personally, I prefer the condition-based color changes: white when it's snowing, blue when it's sunny, dark gray during rain, and so on.
AeroWeather doesn't mess with your wallpaper, fonts, or anything like that--it merely changes Aero's colors. Pretty nifty, don't you think?
The program is compatible with Windows Vista and 7, both of which must have Aero enabled. It also requires the .NET Framework 3.5 (which it will install for you if you don't already have it).
(Note: The installer is called Setup.exe, which can be confusing. Learn how to rename Setup files so they're easier to figure out later.)