Is there any concept of a layer having a background color? If I want to create a solid or gradient background, must I add a rectangle? If so, is there some way to magically resize a rectangle to match the canvas size?

Thanks!

Layers can't have a background so you have to create a shape.

I don't know of a way to quickly create a shape at the size of the canvas, but I always just make my shapes larger than than canvas. Since you only see the canvas area when viewing an SVG in a viewer it doesn't matter that the shape exists outside the canvas.

I don't know of a way to quickly create a shape at the size of the canvas

We probably have different concepts of "quickly" But I would just create a rectangle, and enter the canvas size (Doc Properties > Page size or Custome size) in the tool control bar.

But you're right, the viewer will only show the page size anyway

Why not use 'Snap to the page border' as snap target for bbox or nodes?

If you don't need many layers having different background color you can change the background of the whole document in Document Preferences. Don't forget to shift the opacity to 255 as the default is fully transparent.

Thank you all very much! That's just the info I needed. Much obliged.