How to change color and size of pie chart's default labels in Google Image Charts?

Is it possible to change color and font size of default pie labels (in this simple example: "Hello" and "World") in Google Image Charts API? I've searched the documentation but I can't figure out how to do it...

Example code:

https://chart.googleapis.com/chart?cht=p3&chd=t:60,40&chs=250x100&chl=Hello|World

https://chart.googleapis.com/chart?cht=p3&chd=t:60,40&chs=250x100&chl=Hello|World&chxs=0,008000,16&chxt=x

You define chxt=x Then you set the color using chxs in this format

chxs=0,{color_code},{font-size}