>>530731272
If it's glowing yellow that means you will get a bountiful chest spawn which you need a bountiful key to open.
If the door is no longer yellow after you run it once, that means your chest will no longer spawn until the bountiful delve rotation next day.
The door will stay sparking with thunder for 24 hours until over-charged delve rotation the next day. You can farm the sparking over-charged delve as much as you want to just grind out your full talent tree and get your mount