Rescaling axes on a color table bar

I am trying to create a colored scale bar to use for a waterfall plot of several diffraction spectrum. Each spectrum was taken at a different concentration value, and I have colored each trace accordingly. I want to create an image that plots the color as a function of this concentration.

I have attempted to do this as follows:

<br />
Make/O/N=(256,30) cbar=p*(0.672/254)<br />
Display;AppendImage cbar<br />
ModifyImage cbar ctab= {*,*,ametrineCTAB,0}<br />
End<br />

The resulting plot is attached.

It seems that the x-axis runs the range of the index of the wave, rather than the values in each column (which run from about 0 to 0.7). I have tried using SetScale to change this, but nothing seems to happen. A 3d surface of this color bar image seems to have the z-values running from 0 to 0.7, however.

How can I change the x-axis scaling to reflect the correct range of values?