#00F is the same as: #0000FF and is BLUE.
#FF0 is the same as: #FFFF00 and isYELLOW.
#6B5 is the same as: #66BB55 and is THIS COLOR.
#000 is BLACK. #FFF is WHITE.
#666 is a DARK GRAY. #AAA is a light LIGHT GRAY.#FF0000 means FF worth of Red, and no Green or Blue. The result is RED.
#0000FF means no Red or Green, and FF worth of Blue. The result is BLUE.
#FFFF00 means FF worth of Red and Green, and Blue. The result is YELLOW.
#000000 means no Red, Green, or Blue. The result is BLACK.
#FFFFFF means full FF amounts of Red, Green, and Blue. The result is WHITE.
#FFEFD5 has high values for all colors, giving a light result: PAPAYAWHIP.
(no, I don't know who thought up the color names.)
#556B2F has lower values for all colors, giving a darker result: DARKOLIVEGREEN.
#FFEFD5 (PAPAYAWHIP) and
#556B2F (DARKOLIVEGREEN)
...are not web safe colors. They would get shifted to
#FFFFCC (NOT PAPAYAWHIP) and
#666633 (NOT DARKOLIVEGREEN)