In SolidWorks, you can assign material to the construction profile with Weldment profiles.

However, for the operation to be successful, you have to assign this material to the profile beforehand.

Defining the material looks the same as in the case of 3D objects.

Then, if you choose a profile with the material Transfer the material from the profile. If no material is specified in the selected profile – An error will appear.

Of course, this default material can be removed or changed to another at any time.