edge 520 workout screen

I looked around the site looking for documentation about the information shown on the screen of a garmin edge 520 unit during a workout w/o any luck. So couple of questions

In the picture below what is the meaning of the upright bar that is in the middle of the screen on the right (mine is multicolored)

Why does sometime during an interval below “PWR” it will show “SMART” and the values will turn purple while other times it shows “SMART” but the values stay black?

thank you

Purple means that the interval is based on you reaching an target MPA value. Duration is variable. If it’s black, the power is variable.