we are using GXT 2.2.x for over a year. Now, we are evaluating GXT 3 (3.0.0b). We are excited about the GXT 3 Charts. I used the Pie Chart example (http://www.sencha.com/examples/#ExamplePlace:piechart) to do some tests. I encountered a problem with specifying colors for a PieSeries. Maybe I'm doing something wrong.
Instead of specifying a gradient, I tried to specify a HSV and HSL color, respectively. In both cases the pie chart has black segments. Using RGB colors the pie chart is rendered with the specified colors. To isolate the problem I used the following code:

series.addColor(new HSV(new RGB(148, 174, 10)));    // Black segment
series.addColor(new HSL(new RGB(148, 174, 10)));    // Black segment
series.addColor(new RGB(148, 174, 10));    // Works fine
With the aid of Firebug: the following SVG paths are created within the resulting HTML:

<path d="M172.0,230.5 L143.39205047240992,111.90158001125454 A122.0,122.0,0.0,0,1,278.08990550028653,170.25938288048275 Z " stroke-width="0.0" fill="hsl(69.51219512195121, 0.891304347826087, 0.3607843137254902)"/>
<path d="M172.0,230.5 L185.10052429302795,351.7945846410621 A122.0,122.0,0.0,0,1,52.813503881183834,256.5495516836551 Z " stroke-width="0.0" fill="hsv(70.0, 94.0, 68.0)"/>
The "fill" attribute uses the color specification hsl() and hsv(), which leads to black segments. In case of rgb() the respective segment is colored correctly. Are hsl() and hsv() allowed SVG color specification?