fiskeben

This plugin adds a simple way to let your readers enable or disable a high contrast stylesheet for the visually impaired.
Once a reader enables the high contrast stylesheet the setting will be stored in a cookie which means the setting will not only stay one when navigating to other pages but it will also be on when the reader returns.

Vividly

Enables toggling an extra stylesheet with high contrast CSS for visually impaired users.

Robert Chapin

Input fields on the WordPress admin screens have been nearly invisible since version 2.7. After a year of hacking CSS files to work around this problem, Matt suggested I make a plugin to override core CSS values. This plugin does just that.
Fix Admin Contrast now also corrects white point issues on iPad and similar displays. Without this plugin, the administrative table colors can look the same as the background color.
If you need even more contrast, consider my plugin called <a href="https://wordpress.org/plugins/high-contrast-admin/" rel="ugc">High Contrast Admin</a>

Fix Admin Contrast

Improves the visibility of administrative form fields and tables.

Vividly vs Fix Admin Contrast