color: use ui.formatted() to test TTYness, not sys.stdout.isatty() This fixes the color extension not working with pager (broken in 877390020477). The pager extension already sets ui.formatted=True to allow this use case.

from hgext import color

# ensure errors aren't buffered
testui = color.colorui()
testui.pushbuffer()
testui.write('buffered\n')
testui.warn('warning\n')
testui.write_err('error\n')
print repr(testui.popbuffer())