Getting a color bar from a normally equalized grid (grdhisteq) that reflects the original grid units not the variance

By using grdhisteq I get a way better-looking grid, however, I have been struggling to find a way to create a CPT that reflects the grid unit rather variances (-3 to 3 - normal equalization). It would be great if I could plot a color legend that informs the actual unit of the grid but still having the grid normally equalized. Any suggestions on that?

All the best.

Fabiano