A histogram has nothing to do with how the scale is displayed !

Guess what you want to implement is a multi bar item ( several y values for one x value displayed as a block of several bars with different colors centered to the x-position ). Such an item doesn't exist in Qwt, but it is not so hard to be implemented - as long as you have a solid background with Qt.

I recommend to use Qwt 6 and to derive from QwtPlotSeriesItem.

Uwe