Now the "color" tag is working.
color = any of these [blue, cyan, green, lime, purple, red, gray, charcoal]
Also you can use the "help" tag to describe your blocks.
Example:
<palette>
<block tag="test-print" spec="print %0 to console %1" code="Test.print(~); /* Testing: ~ */" type="action" color="purple" help="Print some text to console." returns="void">
<fields>
<text order="0"></text>
<dropdown order="1">
<choices>
<c text="Pressed" code="1"></c>
<c text="Released" code="2"></c>
</choices>
</dropdown>
</fields>
</block>
</palette>