Yes, you can! Check out the image below for an example.
This is a treemap of sales by business categories and subcategories. The business categories are the distinct colors (green, blue, orange) and the sales value determines the color intensity.
Want to learn how to do this yourself? Check out this video:
Links referred to in video:
How to build a Treemap in Tableau
How to Create Custom Color Legends in Tableau
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