And...just in case the reason you want white is because you want to see a completely white foam-board representation of your model:
As stated by Juha, materials are linked via their index numbers, not their names. In Attribute Manager, you can create a new set of materials that have a white foam look (or whatever) assigned to all index numbers, just by duplicating one acceptable material. Save that set. Then, you can use Attribute Manager to swap between that set of materials, and the default (or other custom) set - letting you show your model as white foam to the client during preliminary phases and switch to real materials at any time. [This method works best if your materials are assigned by function - such as "Exterior Wall" rather than as finish, as in "Brick".]
If that's not what you were thinking of ... sorry for too much information!
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB