When you view Explorer or program windows, specially when viewed from an angle, the subject behavior occurs.
Some monitors DO NOT display the Use Visual styles on windows and buttons on the Performance Options dialog properly. It is generally more noticeable when the Settings tab of Display Properties is set to Medium (16 bit).
To resolve this problem:
1. Right-click My Computer and press Properties.
2. Select the Advanced tab.
3. Press Settings under Performance.
4. Select the Visual Effects tab and press Custom.
5. Clear the Use Visual styles on windows and buttons box.
6. Press Apply, OK, and OK.