public void setColor(int start, int end, ColorRGBA color) {
        letters.setColor(start, end, color);
        letters.invalidate();
        needRefresh = true;
    }
Set the color of substring.
@param start start index to set style. inclusive.
@param end   end index to set style. EXCLUSIVE.
@param color the desired color
jme3-core/src/main/java/com/jme3/font/BitmapText.java