Excellent. As additional explanation, these are the 3 values the Blizzard threat api returns. The loosely tanked ones will show up during tank switches, especially if something goes wrong or during taunt while one tank is building up aggro.
The (red) ones show up usually when adds arrive and initially target random people by proximity, heal aggro, etc. On boss fights I do not recall ever seeing it before a non tank pulls aggro and gets one-shotted. In toc vs the pvp bosses you will see a lot of it as well.
Is there a way to disable the blinking effect of the threat indicator? I find it really distracting (in a negative way) when the square itself was enough. i couldn't find anywhere to set blink for Threat though.
ETA: it would be ok if it just blinked when someone pulled aggro, but it blinks even for tanks for me. Is this normal behavior? I've reset my settings as well.