You have a TabObject in your table? Your question would be better posted in
the microsoft.public.access.forms newsgroup.

The only way the tab control becomes "transparent" when you change the
control's Back Style property to "Transparent" is if the
tab control's Style property is set to "None". Otherwise, so long as a tab
or button is used as the style, the control will not be transparent in form
view.

I've also seen information that says you can get transparency if you
uncheck:
   Tools | Options | Forms/Reports | Use Themed Controls

and if you turn off Windows XP Themes.