One of the first things we all learn how to do, as we begin our foray into education, is count. From the earliest rhymes ("One, two, buckle my shoe..."), to childhood games (remember jacks?; I could never manage "eightsies"...), to math in school, counting is an integral part of everything we do. Our normal counting system is based on the number 10, meaning that there are ten units that can be represented by a one digit number, before we have to go to a second number. Those numbers are:
0
1
2
3
4
5
6
7
8
9
Then, when we get to the number after 9, we start back over at 0 (in the one's column), and precede it with a 1 in the ten's column: 10. So that a large base-10 number can be broken down as follows:
937
7 ones =
7
3 tens =
30
9 hundreds =
900
The hexadecimal numbering system is based on exactly the same concept, except instead of using 10 as a base (remember base-10?), the hexadecimal system uses 16 as a base. So hexadecimal numbers are also referred to as base-16 numbers. Instead of creating new characters to stand for the new numbers, we use the first 6 characters of the English alphabet. Therefore, the hexadecimal numbering system is based on the following 16 characters:
Hex
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
Dec
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Then, when we get to the number after F, we start back over at 0 (in the one's column), and precede it with a 1 in the sixteen's column: 10. So that a large base-16 number can be broken down as follows (converting to decimal):
C4E
E ones =
14
4 sixteens =
64
C 256s =
3072
C4E (Hex) = 3150
I created the following tool using JavaScript to help you convert the decimal numbers given by most graphics programs. Just enter a decimal number on the left, and click Convert.

Dec2Hex

Decimal
Hexadecimal
Enter a decimal (0 - 255) or a hexadecimal (00 - FF) number in the appropriate box, and click the Convert button. Click Clear to clear the form.
Colors in HTML are expressed as RGB triplets, generally expressed as #CC66FF. These triplets are made up of three two-character hexadecimal numbers (one for red, one for green, and one for blue), which can take the value of #00 to #FF (0 to 255, decimally speaking). The total number of colors that can be displayed by today's major browsers is:

256 * 256 * 256 = 16,777,216

Pretty amazing, huh?.