Who needs colors? Karn don't need no colors! I got an answer to everything right here. Now if I could only find that tutor...
That list is an awful big pile of artifacts, so I will use this space to address some of them with a little more detail. Karn wants to win by using an infinite combo, smashing people with big creatures, or locking down the board and fighting with animated artifacts. This is a tool box deck, it has removal, board wipes, counterspells, land destruction, taxes, card draw, and tons of mana to use it all with. The only problem is finding the solution to the problem at hand.
General: Karn, Silver Golem. Karn can turn artifacts into creatures. Use them to attack and block, use them in combos, remove equipment from enemy creatures. The possibilities are endless.
Voltaic Construct: I could write a book about the uses of Voltaic Construct. This is easily the most powerful card in the deck. This is what you tutor for almost every time. The combo looks like this: Karn animates a mana artifact that is able to produce at least 3 mana. Tap it or 3 mana, use 2 of that mana to untap it with Voltaic Construct. Repeat for infinite mana, adding 1 each time. You can now end the game with Goblin Cannon for infinite damage. If you are feeling creative, animate Prototype Portal and untap it infinitely for more artifacts, or destroy an infinite number of permanents with Lux Cannon. Heck, Lets use planar portal to tutor every card out of the deck and do all of these things. Voltaic Construct wins games.
Lands: Most of these are just colorless lands, many have an ability. Most of them aren't worth mentioning, but a few prove routinely important.
Eye of Ugin- Tutors are good. No I mean, like really good. Go back and read what Voltaic Construct can do in this deck, and then think about how handy a creature tutor is.
Urza's Mine, Powerplant, and Tower- These are fluffy. I don't think I have gotten them on the board together since we lost the ability to steal Primeval Titan from other players, but they are fun and fluffy.
Homeward Path- Blue players like to take your artifacts. Take them back.
Desert- Too much fun to kill someone's creature with 1 spiteful little damage
Stripmine and Tectonic Edge - You need to be able to kill lands. This is a good way to do it
Thespians Stage and Vesuva - This deck is a toolbox. These lands can be any tool you want them to be. That's awesome.
Buried Ruin - Colorless recursion is hard to come by. Getting a card back after removal will always be valuable.
Phyrexia's Core - Plays nice with Spine of Ish Sah
Mana Rocks: These tap for mana, and Karn lets us use them to attack as well. This deck runs so many mana artifacts that we can cut it down to only 35 lands. The main thing you are looking for in your starting hand is a decent curve of mana artifacts.
The boring ones just make mana - gilded lotus, ur-golem's eye, fractured powerstone, mind stone, sol ring, thran dynamo, pristine talisman, worn powerstone, basalt monolith, sisay's ring, fellwar stone, dreamstone hedron
Doubling Cube - Whats more fun than a butt load of mana? Two butt loads!
Blinkmoth Urn - This card gets pretty silly right about the same time you can cast it. Aside from infinite combos, this is the best mana source in the deck.
Krark Clan Ironworks - Mana for emergencies, and a sac outlet when you need it as well.
Board Control: These things make it harder for the table to get way ahead of you. They need to be played strategically. No point in making everybody gang up on you because of a turn 2 Winter Orb. If you get a few of these in play, Karn can settle in for the long game and dig for combo pieces or attack with animated artifacts.
Torpor Orb - Stops all those annoying ETB effects that get used over and over again.
Winter Orb - This card draws hate like no other. That said, we aren't using colors here. I find that I often use this to attract counterspells. 2 mana is a cheap investment to make sure a combo piece makes it to the board. Edit: after a long time in the deck, eventually cut this guy.
Storage Matrix - This is winter orb light. If you have a way to tap it, you can even avoid the negatives on your own turn.
Icy Manipulator and Ring of Gix - Tap down their mana, tap their blockers, etc. They seem mana intensive at first, but they will win games.
Arena of the Ancients and Meekstone - Don't let other players run rampant with their big creatures. These 2 cards can keep a lot of Voltron Generals from swinging.
Portcullis and Ward of Bones - Don't let other players put stuff on the board. These cards can make your board wipes permanent. If karn is currently the only creature on the board, respond to everything they cast by animating an artifact to hit the 2 creature limit and force their creature into exile.
Null Brooch - Counter their stuff. Combine with an untap effect for extra control
Lodestone Golem - Tax their spells.
Utility: This is a catch-all for all those things that let us be tricksy.
Mycosynth Lattice - If you feel like being a jerk, this card lets Karn turn lands into 0/0 artifact creatures. If you're not a jerk, you can find other creative things to do with a board full of artifacts.
Vedalken Orrery - Oh, you'd like to wipe all artifacts? I'll go ahead and flash in Mycosynth Lattice...
Sculpting Steel - Clone is GOOD
Jester's Cap - Pull combo pieces out of other player's decks.
Darksteel Forge - Think about what happens when you put this on the board with Mycosinth lattice.
Clock of Omens, Voltaic Key, and Unwinding Clock - Use these to abuse all of those cards that you were only going to activate once each turn.
Cloud Key - Yay, Discounts!
Prototype Portal - Make lots of artifacts. I have used this in conjunction with Rings of Brighthearth and Clock of Omens to generate infinite lodestone golems...
Trading Post - This card has so much utility. Most importantly, it is one of the only ways to get stuff out of the graveyard. Also, GOAT TOKENS!
Myr Retriever - The last way to get stuff out of the yard.
Mirrorworks - Yay, Extra stuff!
Steel Overseer - This guy can partner with animated artifacts to act as a back up win condition. Don't forget that they don't lose the +1/+1 counters when they stop being creatures for the turn.
Rings of Brighthearth -This card combos with basalt monolith for infinite mana. You can also useit to double up on pretty much any ability in the deck.
Big Beater Creatures - Big stompy creatures are our secondary win condition.
Blightsteel Colossus - Blightsteel gets stolen out of my deck more than any other card, and it really hurts when they use him to eliminate you. That said, Blightsteal + Greaves is a mean thing to do to an opponent.
Darksteel Colossus - Big stompy dumb guy. What can I say, I like Iron Giant
Ulamog - Accelerate into him early for an easy win, or tutor him late game for uncounterable removal.
Kozilek - karn will never draw enough cards or use enough annihilator triggers. Kozilek does both.
Removal and Board Wipes -
Done for the night, I'll finish thinking later
