I am sure this is an easy question but I could not find the answer anywhere… so once again I am looking for your help

I have a histogram with a color axis which I drew with COLZ. However the numerical values corresponding to these colors are very high (the legend goes from -5e10 to +1e10) so I am looking for a way to display them in scientific notation.

I tried to go using TGaxis but apparently the color box is not considered an axis