The hex color #21b4fe is a light color. The web-safe version is Hex
#33CCFF. A complementary color is
#DE4B01. The grayscale version is
#9C9C9C. A 20% lighter version of the original color is
#54E7FF, and Hex
#0081CB is the 20% darker color. If the color is saturated by 10%, you get
#15B6FF. If the color is desaturated by 10%, the color
#2DB2F4 is obtained.