Turn off the red triangles (collapse/expand indicators)

I would like to turn off the red triangles which appear in my first column to the left of the schedule area. How can I do this?

Just un-check the Collapse/Expand Indicators option on the View tab.

Change the color, size, shape of the collapse/expand indicators

Available shapes:

Down Triangles		shows a filled downward pointing triangle to indicate the task is rolled up. Shows a non-filled downward pointing triangle to indicate the task is not rolled up.
Down/Right Triangles		shows a filled downward pointing triangle to indicate the task is rolled up. Shows a filled right pointing triangle to indicate the task is not rolled up.
Plus/Minus		shows a filled plus symbol to indicate the task is rolled up. Shows a filled minus to indicate the task is not rolled up.