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.
Regarding how to switch to these themes, please see ZK Developer's Reference/Theming and Styling/Understanding the Theming Subsystem/Switching Themes ß