The hex color #664d37 is a dark color. The web-safe version is Hex
#666633. A complementary color is
#99B2C8. The grayscale version is
#4E4E4E. A 20% lighter version of the original color is
#99806A, and Hex
#331A04 is the 20% darker color. If the color is saturated by 10%, you get
#684D35. If the color is desaturated by 10%, the color
#644D39 is obtained.