Discrete vs Continuous –
There is a big misconception that blue color represents dimensions and green color represents measures. But this is not true. In Tableau, the blue color represents that a field is discrete and green color indicates that a field is continuous.
If I drag and drop sub-categories to Rows and Sales to Column, you can see that sub-category is represented by a blue color and sales is represented by green color.
Another way you can distinguish whether a field is discrete or continuous is the way it is represented when you drop a field to the colors inside the Marks card.
If I drag and drop category to the color inside the Marks card it will be represented like this. You will see different colors of the bars when a field is discrete.
But if I drag and drop sales to the color inside Marks cards, you will see a single continuous color scale.
Another way to distinguish between two is that when a field is continuous it is aggregated by some functions like SUM, AVG, MIN, MAX compared to discrete which is not.