Fusion uses color to indicate when areas of a model exceed upper and lower tolerance values, so you can easily see where the model may have too much, or too little, material after machining.
Historically, Fusion used the same colors differently in stock simulation and surface inspection. For example, in stock simulation, red indicated below tolerance, but in surface inspection it denoted above tolerance.
Example of stock simulation using tolerance colors.
Recognizing the potential for confusion, Fusion now uses the following default color convention for both stock simulation (when using the Colorization option of Comparison) and surface inspection results:
If you prefer to swap how red and blue are used, you can select an alternative color convention.