Need some help on understanding how this watchface color is implemented?

I like the look of this watchface but hope to customize it a bit.

Specifically, for the gradient color background, I think I can create a png file as background, but I don't know how to make the minutes and days of the week/days of the month to have the gradient color.

I don't see any api to support fill with gradient color. Is it related with the alpha blend mode on a buffered bitmap?