1. No precise colors.
The best thing to acknowledge-colors you use on the web page won’t look similarly on all monitors. This happens because of a variety of causes: monitor’s brand, the bit-depth or in case of notebooks and tablets-the angle of the screen. I recommend you use safe colors as much as possible.
2. Test alternative Gamma settings
If you design web pages on Macintosh, a special attention should be put on testing the designs for Windows machines. To see how your design will appear on a Windows computer, you can set the brightness darker in the System Preferences. If the image is too dark or too light make some adjustments and fix the image’s brightness. Another method is to test your images in Photoshop: go to View > Proof Setup > Windows RGB (or Macintosh RGB if you’re actually on a Windows machine.)
3. Use transparent images for the background
Though on 16-bit monitors a considerable discrepancy appears between background and foreground, use a transparent PNG or GIF to make sure there is no rectangle around your image on old monitors.