Can the button on my 404 page send shoppers to my sale page instead of the home page?

Yes. You can change the button's link and text.

1. Go to Settings → Web Settings → 404 Page Settings.
2. Click the design you use under Choose a design.
3. Make sure Show “Back to home” button is on.
4. In Button text, type something like See today's offers.
5. In Button link, enter the page address, for example /shop or the web address of your sale page.
6. Click Save Changes.

The button colours are in the same form. Only the design that is highlighted when you click Save Changes is saved and shown to shoppers, so make sure it is the one you want live.