What do all these numbers mean?

The numbers show the four different ways the same color can be specified by number in CSS:

Hexadecimal value: The traditional six-digit hexadecimal notation.
Three-digit hexadecimal: If the six-digit hexadecimal number is made up of three repeating pairs, this shorthand form can be used. (moreCrayons uses the three-digit hexadecimal notation extensively to reduce file size.)
RGB [0–255]: Red, green, and blue expressed as values from 0 to 255.
RGB [0%–100%]: Red, green, and blue expressed as percentages. (Some of the percentages are slightly off due to rounding.)