Hi @Thierry_S
The color map in Clustering > Hierarchical operates in much the same way as the Graph > Cell Plot. There is control over the gradient in general terms (right-click a cell in the color map > color theme), but this implementation lacks the fine-grained control you see in say Graph > Graph Builder, where you can specify not just a theme, but a lightness range, number of levels, min, center, and max, etc.
But I have some good news for you. Hierarchical does honor the Color Gradient property that you set for a column in Column Properties (right click column > column properties). So, set your specific gradients there, where you can specify not just theme but min/max/center, and then when you request the color map in Hierarchical you will get your column-specified gradients (regardless of what you pick in Hierarchical).
I hope this helps!
@julian