Another possibility to use differently colored balls, is to use the original images and recolor them with ColorMatrixN options. For example, if add a to all of [MeterLeft], [MeterLeft2], [MeterCenter], [MeterRight2] and [MeterRight] meters, you'll get all those balls yellow. Any color is possible, just have to find the proper ColorMatrxN options and apply them.
This method has a great advantage: it doesn't require image manipulation. A bit later I'll work with this and will post a sample code.