css - How does hexadecimal color work?

Question

What does the hexadecimal that represents a CSS color mean? How can I tell what color it is without memorizing the exact code? Does it have any relationships with RGB (and CMYK) system?
I thought for a moment that FF means 255 in RGB, but then I realized that 15^2 isn't 255, but 225.

Answer 1

Hexadecimal uses sixteen distinct symbols, in the case of css color the symbols 0–9 to represent values zero to nine (obviously), and A,?B,?C,?D,?E,?F to represent values ten to fifteen. So, using one Hexadecimal character you can represent 16 values. With two Hexadecimal you can represent 256 (16*16) values.

In RGB you have colours represented by Red Green Blue (R=0-255, G=0-255, B=0-255), so we use 3 pairs of Hexadecimal symbols! So when you see an RGB color, you can make the calculation below.

Example:

Hex: #4C8ED5 is RGB: 76, 142, 213.

Because 4C = 76(Red), 8E = 142(Green), D5 = 213(Blue)!

Hope it helps your understanding!

More to read: Hexadecimal on Wikipedia and a nice RGB to Hexidecimal Converter