If the texture or color thumbnail for the SKU selected is not available, it will display as a clear checkerboard pattern placeholder on the Samples Preview.
You can select a thumbnail and save it to the SKU for future use. See Set Texture, Set Solid Color, Set Color Core, or Set SKU by Color below.
SKUs
The Frame and Mat SKUs (Stock Keeping Unit) for each Frame/Mat can be selected within the software from Subscribed Vendors.