What is the format of the color-map file?

[ajaynair]

This is green.txt. What does each entry here mean?

0.0 0.0 0.0 1.0
0.1 0.4 0.2 1.0
0.2 0.6 0.3 1.0
0.3 0.7 0.4 1.0
0.5 0.8 0.4 1.0
 
0.5 0.8 0.4 1.0
0.3 0.7 0.4 1.0
0.2 0.6 0.3 1.0
0.1 0.4 0.2 1.0
0.0 0.0 0.0 1.0

A link to an article that explains this will be great too. I searched online but I couldn't find much help. I am guessing I am not using the right search terms.