I changed the company's default layout style, but why hasn't one of my catalogs updated? Why is the layout still the old style?

That catalog has its own layout style setting. The rule is: if the catalog has its own setting, use that; otherwise, use the company default. Brand color always uses the company color regardless. To change that specific catalog, go to Product & Catalog → Product Catalogs page → click the catalog name to enter the layout editing page. In the "Catalog Settings" card, select a layout style under "Layout Style," or click "Use Company Default" to make it follow the company default again. It saves with a single click, and the preview on the right updates immediately to the new layout. There's no need to upload changes. Note: Each catalog can use a different layout style and grid size, but all catalogs must use the same color, which is the company-level brand color.