Filled Map Colour Saturation With Legend

Hi 

I am trying to create a map which shows how the map of Spain is split between our 3 sales managers. I can use the legend option to seperate the three regions into different colours like so:

Within my data I have the number of leads generated in each province within each of the three zones. Is there any way to create a colour saturation for the provinces in each zone depending on the number of leads generated? So for example in the west zone can I have different shades of yellow depending on the leads generated?

Thanks!