Can you distinguish four patches in each of the above images? If not, or they have a color cast, then you need to calibrate your monitor.
Stand ten feet from your monitor and examine the above figure. If the smooth patch is darker or lighter than the background then you need to calibrate your monitor.
Many computer monitors come from the factory preset for an office working environment which may not be ideal for viewing and editing photographic images. For color accuracy and consistency work in a darkened environment.
It takes just a few minutes to make these adjustments. As a reward you will view images on the web as they were designed to be viewed. If you're a web designer, or share images with others, then it's imperative that you calibrate your system to a standard. For the web or email use the sRGB standard.
The sRGB standard specifies a color temperature of 6500°. Most monitors have provisions for setting color temperature using on-screen menus. Be sure to set monitor color temperature before calibration. Also check that your display is configured for 24 or 32-bit color. With 16-bit color there is not enough color depth to calibrate properly. Let your monitor warm-up for at least 15 minutes before calibration.