WordPress latest upgrade is probably for security reasons, but like all software updates, every small change in code ALWAYS affect existing code elsewhwere in the programme.

The following should help you restore your headers:

Each Theme has it’s own particular Header size restrictions:

Go into your WP ADMIN

Select CUSTOMIZE

Check or resize your header is compliant to the WP recommended size.

SAVE and PUBLISH

NOTE: This may rquire repeating several times but please allow 10 minutes or so between repeats – it WILL eventually appear.

Each Theme has it’s own particular Colour Schemes:

Go into your WP ADMIN

Select CUSTOMIZE

Find a colour scheme you like by clicking on those available and seeing it on the preview.

NOTE: I think only those marked FEATURED may be Free, all the others may be PREMIUM.

WordPress SHOULD notify you beside the SAVE and PUBLISH Button at the top of the options.

This may not restore your original Background, but WP are working on this issue.

Hope this helps, but please be reminded that I am only an Ape, NOT a WordPress Expert 😀