Windows 7 does comes with a default sticky notes application, but in case you want some more customizations, then you can try out Metro Pad. It is a freeware app for Windows which can be used as a sticky notes on your desktop. The app is portable and allows you to do a bit of customizations like background color, aero (transparent background) and also has options to change font and font colors.
You can change the background colors from the available list of colors or pick your own color.
You can move the sticky pad on your screen by dragging the edges.
The app is compatible with Windows XP, Vista and 7.
