High Contrast Theme
From Documentation
ZK provides 3 high contrast themes according to WCAG 1.4.3 Contrast (Minimum): The visual presentation of text and images of text should have a contrast ratio of at least 4.5:1. When we design these themes, we rely on Sketch Accessibility Assistant to ensure each theme conforms to WCAG 2. After that, we have verified them using axe - Web Accessibility Testing.
Regarding how to switch to these themes, please see ZK Developer's Reference/Theming and Styling/Understanding the Theming Subsystem/Switching Themes.