An easy to understand explanation of the codes is also available

Printable PDF version

Developed in the early 1940s, (see note at bottom) this color code uses only 10 colors divided into 5 group colors and 5 pair colors.
 Tip + Ring -
1st group White
blue

1st pair
orange

2nd pair
green

3rd pair
brown

4th pair
slate

5th pair
 
2nd group Red
blue

6th pair
orange

7th pair
green

8th pair
brown

9th pair
slate

10th pair
 
3rd group Black
blue

11th pair
orange

12th pair
green

13th pair
brown

14th pair
slate

15th pair
 
4th group Yellow
blue

16th pair
orange

17th pair
green

18th pair
brown

19th pair
slate

20th pair
 
5th group Violet
blue

21st pair
orange

22nd pair
green

23rd pair
brown

24th pair
slate

25th pair
 
 
This solid color code actually goes up to 25 pair, however, the colors will frequently vary from one manufacturer to another on pairs beyond white-blue
Old Color Code
Tip + Ring -
green     red
black     yellow
white     blue
brown     orange
pink     gray
Ethernet Color Codes
Click for enlargement
Click for enlargement 24 k
Pin Fnctn Pair type A*   type B*
1 TX+ 2

2 TX- 2

3 RX+ 3

4 1

5 1

6 RX- 3

7 4

8 4

Function refers to NIC (network card) pins
* It doesn't matter whether you use type A or B but to avoid confusion you should use the same type throughout your network
Category 3, category 5, what's the difference?
Click for more info
International color coding for UL-/CSA-Control Cable
1 black
2 brown
3 red
4 orange
5 yellow
6 green
7 blue
8 violet
9 grey
10 white

(Note)
Jim Stettler wrote me in November of 2001 with the following comments. Thanks Jim.

"I used to have a telephone manuel from the late 30's-early 40's that had the standard (current) Color code. The determining factor for using the colors that they did, had to do with the ease of identification along with the availability of dyes for cloth cordage. IE they wanted cheap easy to use dyes that were easy to identify." .