Treemap Color Customization

I am attempting to create a treemap that contains information on wells within various stations in a water system. In this case, I am interested in the % specific capacity remaining from the original specific capacity. I did this by creating a calculated column that then groups the data points into 4 common % gradients. I want to put this into a treemap so that each gradient has its own distinct color.

This is my manually drawn mock up in PowerPoint:

The large numbers represent the Station No. which is the "category" in the treemap settings (I was able to achieve this in PowerBI). The small % values in the corners of the squares represent the % of wells within each respective station that are within that % specific capacity gradient (currently in my PowerBI version, the corner values are just the respective % gradient). Each % gradient has its own color as shown in the legend.

This is what I was able to put together in Power BI:

I am not as concerned about placing the % of wells within each station that are in X % specific capacity gradient, as my main priority is figuring out if there is a way to make the treemap coloration based on the field that is placed within the "details". Currently it is colored by category. I am curious as to if anyone knows if this is possible?