High Contrast lets you browse the web with your choice of several high-contrast color filters designed to make it easier to read text.
When you install this extension, all pages are "inverted", so black becomes white and white becomes black. Press the "browser action" icon in the toolbar to toggle it on and off, or customize your settings on a per-site basis. Use a convenient keyboard shortcut to quickly change your settings while your browse.
Other extensions try to change the default colors, but this ends up breaking many popular websites. Only this extension applies filters to your page that invert almost everything - the only exception is photos, which are left alone.
Also note that the Chrome web store and other built-in pages like the New Tab page and Settings pages are unaffected - extensions like this one are not allowed to modify them, by design.