suddenly my safari page appears all black

I have seen users describe Safari as being "grey" but black is a first for me ....

Quit Safari. From the home screen - Double tap the home button and find the Safari icon in the task bar. Tap and hold down on the icon until it wiggles, then tap the red minus sign. Tap the screen above the task bar. Try Safari again.

Or do you mean that the app border is black in color now? That indicates that private browsing is turned on. settings>Safari>Private Browsing>On. If you turn it off, Safari will be the regular grey color again.

Try clearing Safari's cache : Settings > Safari > Clear Cache (and Clear History) - it's 'Clear Cookies and Data' on iOS 5

If that doesn't work then try closing Safari completely and then re-open it : from the home screen (i.e. not with Safari 'open' on-screen) double-click the home button to bring up the taskbar, then press and hold any of the apps on the taskbar for a couple of seconds or so until they start shaking, then press the '-' in the top left of the Safari app to close it, and touch any part of the screen above the taskbar so as to stop the shaking and close the taskbar.

A third option is a reset : press and hold both the sleep and home buttons for about 10 to 15 seconds (ignore the red slider), after which the Apple logo should appear - you won't lose any content, it's the iPad equivalent of a reboot.