Hello,
I think I understand your misunderstanding of the graphs :
In fact you shouldn't read the different curves as beeing represented on the same graph, and thus adding their max to compute your total bandwidth, but the total bandwith used by the queues is the skyline, the out shape of the curve, while each color represents what place each queue reprensents in this whole.
So on the former examples you shouldn't read that the mustard queue uses 1 Mb/s, it only uses what the others have let to her, corresponding exactly to the mustard part of the curve you see. There's no "hidden" mustard :-)
Michel