code: public void setThumbColor(int startColor, int endColor) {
          mSeekBarDrawable.setThumbColor(ColorStateList.valueOf(startColor));
          if (mIndicator != null)
              mIndicator.setColors(startColor, endColor);
      }
docs: Sets the color of the seek thumb, as well as the color of the popup indicator.
  
  @param startColor The color the seek thumb will be changed to
  @param endColor   The color the popup indicator will be changed to