I only owned this hat for a few hours :P

Sale #1:

Sold it for 47 keys:

http://m.imgur.com/BzVySb7

Proof of the effect:

http://m.imgur.com/tft6OUj

Sale #2:

Bought it for a Vivid Plasma A Rather Festive Tree and a Strange PDA after the seller added 2 keys and 8 refined:

http://m.imgur.com/BzVySb7

Proof of effect of the Noir:

http://m.imgur.com/c5goyzN

Proof of the effect of the Tree:

http://m.imgur.com/GHR063c

Total: 53.5 keys (No overpay as the Noir was offered:http://m.imgur.com/ECfazDu )

However his buyout was 47 keys:

http://www.tf2outpost.com/trade/26644500

Hence the value caps at 47 keys

Sale #3:

Sold for a Strange Disco Beat Down Anger + Earbuds + Painted Black War Pig:

http://m.imgur.com/ScTE122

Proof of effect of the Noir:

http://m.imgur.com/QjSSen4

Total: ~45.5 keys (after overpay)

Rounding it up to 46 keys

Credits to Gtking616 for the screenshots

Sale #4:

Offered and sold for a Duped Scorching Flames Janissary Ketche and 10 keys:

http://www.tf2outpost.com/trade/26582614

History of the Ketche:

http://backpack.tf/item/733979534

Buyer's backpack before:

http://backpack.tf/profiles/76561198116961063?time=1437721200

Buyer's backpack after:

http://backpack.tf/profiles/76561198116961063?time=1437807600

Total: 46.5 keys (no overpay as it was offered)

Rounding it up to 47 keys

Please tell me if I did anything wrong.