Hello Mazin Barbat,
I'm not sure why you cannot change the background color of all items
in the Task Usage view, including Summary tasks, non-summary tasks,
and assignments.
To speed things up over the 3000 lines, you could use filtering to
selectively hide tasks and then apply the background color to only
the visible tasks. For example, use the "Summary Task" filter
applied to the view, select all tasks (click the select all button
in the upper left corner of the table) and apply the background
formatting for the selected tasks. Then, turn off the display of
summary tasks through Tools > Options, View tab. Again, select all
tasks and apply the background formatting for non-summary tasks. You
could then create a custom filter showing only assignments, and
repeat the process.
I hope this helps. Let us know how you get along.
Julie
Project MVP
Visit
http://project.mvps.org/ for the FAQs and additional
information about Microsoft Project