Certain settings and preferences in Affinity Designer can be adjusted to help make the workspace more accessible, improving visibility of designs, readability of text, and adjustability of tool handles.
Customizing the UI appearance
From the app's settings, you can change the UI style, as well as the UI background, artboard background gray level or UI gamma level, adjusting the contrast to improve visibility.
To change the UI from dark to light (or vice versa):