Abstract from Bruce Lee's proposal
(http://ui.netbeans.org/docs/hi/java_elements_icons/):

....
The icons that currently represent Java elements in the IDE have a variety of
problems, and need to be revamped.  Driving this change are several factors:

   1. Accessibility: Red-green colorblindness is quite common (up to 20% of
males over 40 have some degree of red-green colorblindness), and those users
shouldn't be disadvantaged. 
   2. Accessibility II: 508C3 states few things directly about icons, but the
one clear item mentioned is SubPart B, section 1194.21(i):  Color coding shall
not be used as the only means of conveying information, indicating an action,
prompting a response, or distinguishing a visual element. 
   3. Graphic elements, such as icons, should be visual elements, not letters.
There are many scientific reasons for this, but it is also just good visual
design practice.
...