Image overlay and colormaps

I am using the sc() function to overlay two images

1. a greyscale background

2. an image of pH levels with a custom colormap

( range of values is appr. 2.9 to 4 )

The visual result is as intended, however when I show the colorbar() I get the grayscale bar. I need to show the custom map colorbar. It is also important that the values are not scaled in 0-1 but remain at 2.9-4.

P.S. I have tried using built in cmaps such as 'prob','hot' and I have the same problem.