What is the method behind the O'Reilly book cover color scheming?

The colors are linked to the topics. Here's a general color key:

Web Design/Development: Teal
Programming: Magenta
Perl: Turquoise blue
Java: Dark purple
Apple: Light purple
System and Network Admin: Dark blue
Windows: Royal blue
Security: Yellow
Oracle: Orange
Data: Bright red
Mobile: Grassy green
Linux: Warm brown-red
In a Nutshell references: Rust red metallic

As topics morph and/or grow, we may introduce new colors and retire others. For example, you'll find some Data titles in the Programming group (we will change the color to our relatively new Data red when we reprint those titles).

-Edie Freedman, Creative Director at O'Reilly

This is great -- thanks so much! Your books are gorgeous.