@Override
    public void draw(Canvas c) {
        if (mShadow != null) {
            mShadow.getPaint().setColor(mBackgroundColor);
            mShadow.draw(c);
        }

        final Rect bounds = getBounds();
        final int saveCount = c.save();
        c.rotate(mRotation, bounds.exactCenterX(), bounds.exactCenterY());
        mRing.draw(c, bounds);
        c.restoreToCount(saveCount);
    }
Set the colors used in the progress animation from color resources.
The first color will also be the color of the bar that grows in response
to a user swipe gesture.

@param colors
ptr-lib/src/in/srain/cube/views/ptr/header/MaterialProgressDrawable.java