Just testing the new theme in WP 5 beta1. No header image, and if bg image is used there's no way to change title colour, besides being forced to add bg color or change text color to each block to make content readable if bg image is used. I like minimalist themes, especially in the perspective of creating pages and posts layouts with the new Gutenberg editor, but IMHO theme customization is a must, at least about font and colour choices, in this case.