Civilization – Why is this Civic’s boost bar pink

With Civ 6 replacing happiness with Amenities it also changed how that is awarded. You must now improve the tile to gain it's benefit for the amenity and the second thing to note is that ALL of your amenities will be shared across ALL of your cities automatically. So it would appear that overall, you do not have enough.

Hope this helps.

Edit: 1 luxury resource = 4 amenities.

If you consider only the points you specified, the answer is simple. Just build the mine :).

There are only 2 reasons you should be considering while doing this (hills with forest - bear in mind that lumbermill can also be constructed on tiles without hills but with forest):

• Religion that gives bonuses on forest tiles (I'm speaking from memory but afaik there was one bonus like that)

• Buildings that require adjected forest (I think there was a wonder that require that... same as above, I speak from memory but I think there was one)

• District adjacency bonuses like +1 faith for every two adjacent forest (woods) tiles

And... that's kind of it. This is only considering your exact scenario.

For endgame scenarios, with expanded cities you should read this post: http://forums.civfanatics.com/threads/mines-or-lumbermill.391185/ - apparently in endgame lumbers become better than the mines (it is a civ 5 post but I think it still applies here as well, although a bit less since districts and placed wonders limit the possible space).