The Windows 7 taskbar is awesome in many ways as it comes with lots of features. Now we have a freeware app, RAM Taskbar, which displays the RAM usage as a background color in Windows 7. This app displays the RAM usage in Windows as a progress bar behind it. You can display the physical memory, virtual memory or the total memory in the taskbar. The application is portable and you just need to run the app in administrator mode.
You can set the warning percentage and also the critical percentage to notify you of excessive RAM usage. The color can be changed based on the RAM usage which can be configured.
The application is not complete, there are bugs like it can be closed only through task manager.
Download RAM Taskbar