It seems that when you update the Site Design > Global styles > Text colour field, it doesn't affect all the text. It does affect the headings, page intro and link text (if they haven't been overridden) but not the body text.
It looks like :
.lgd-page-section {
color: var(--color-page-section-text-color);
background-color: var(--color-page-section-background-color);
}
in page-sections.css is taking precedence.