The hex color #effe11 is a light color. The web-safe version is Hex
#FFFF00. A complementary color is
#1001EE. The grayscale version is
#AAAAAA. A 20% lighter version of the original color is
#FFFF44, and Hex
#BCCB00 is the 20% darker color. If the color is saturated by 10%, you get
#F6FF02. If the color is desaturated by 10%, the color
#E8F620 is obtained.