For Quests, if all players have a character with a matching quest step, it's highlilghted in green. If at least 2 have a matching step it's highlighted in blue.
Click on a quest link to pop up a list of all the steps in the quest, with a marker for each character's spot in the progression. Steps with multiple characters are highlighted in blue.
For bounties, click on the bounty name to pop up a list of all the bounty objectives. Completed objectives are highlighted in green.
The Weekly menu includes daily and weekly activities. Completed items are highlighted in green, somewhat complete items are highlighted in yellow.
The Shaxx bounty will show a ? if the user isn't holding the bounty but has enough Crucible rep in the week that it's likely they completed all 5 bounties. This is just a guess, if they did a lot of normal PVP bounties/quests it could be a false positive.
If you have any other questions, suggestions, etc just contact me on reddit, see the info in the footer. Happy hunting, Guardian!