I agree with Bruno (including the point about color and need to have rear lights on, too). In Croatia we don't have DRL, but recommendation is to have your low beams (and so red rear lights too) on at all times. I find I see other cars emerging from the background much sooner if they have their lights on, even in bright sunlight (actually, especially when they are comming from the direction of low sun).

However, Patrick also has a point, too. Obviously, those lights should be automatic in order to avoid this kind of accidents.