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 High Contrast Admin
This plugin is available for download for your site.