Documents where the viewer can adjust features such as size colour font easily

Apple's ideology is mostly to not let the user tweak the design because, in many cases, the user may choose inferior fonts, colors, etc, and thus make Apple production look bad.

Instead of forcing design choices on user, as proudly does Linux and often does Windows, OS X contains settings that Apple considers “best” for everyone.

Of course, some people complain about certain decisions but it's much like MySpace vs Facebook. You can't change fonts and colors on a Facebook page, but frankly, imagine what a mess it would be if anyone could.

Presumably for this reasons, you can't customize how the text looks in input fields, including the login screen.

Perhaps this is too excessive but you could create an AppleScript which would toggle the size of the cursor. To do so just:

1. Go to System Preferences / Universal Access and check Enable access for assistive devices, this will let you use AppleScript to query and control the user interface of most Applications.

2. Go to /Applications / Utilities / AppleScript Editor and paste this code and save it as Application:

   tell application "System Preferences"
   
       set current pane to pane "com.apple.preference.universalaccess"
   
       tell application "System Events"
   
           repeat until slider "Cursor size:" of window "Accessibility" of process "System Preferences" exists
           end repeat
   
           set theSlider to slider "Cursor size:" of window "Accessibility" of application process "System Preferences"
   
           set stash to value of theSlider
           if value of theSlider is 1.0 then
               set value of theSlider to 2.2
           else
               set value of theSlider to 1.0
           end if
           stash
   
       end tell
   end tell