Metalwork Colossus has been one of those cool decks that makes some noise early in a format but doesn't manage to stick around. B/G Delirium and W/U Flash have a stranglehold on Standard right now, and it's tough to break through.
The Metalwork Colossus decks were definitely on my radar for the Pro Tour, but there was a critical issue in how the games played out. Ideally you start on a Prophetic Prism or Metalspinner's Puzzleknot, follow it up with a Cultivator's Caravan, and then land a Skysovereign, Consul Flagship on turn 4. But that only amounts to ten mana in non-creature artifacts, so you cannot immediately cast a Metalwork Colossus.
If instead you have Hedron Archive, you can cast a Metalwork Colossus, but you cannot chain into any more with Sanctum of Ugin, and you haven't interacted with your opponent at all. Your big turn ends up being turn 5, and the deck didn't have to tools to bridge your early game to that turn without falling too far behind.
Playing white gives you Fumigate, which in combination with Cultivator's Caravan gives you a card that can be that bridge. You're not going to cripple your opponent most of the time, but answering a few creatures and gaining a few life will definitely buy you some time to take over the game with your powerful synergies and giant creatures. The other white card, Blessed Alliance, is presumably there to answer Smuggler's Copter, and the option to gain some life is another way to buy time, so I'm a fan.
The other issue with this deck was its weakness to Aetherworks Marvel decks, which are simply doing more powerful things. That deck was very popular at the Pro Tour, but has since fallen out of favor, which is a boon for Metalwork Colossus, although you still see plenty of cards in the sideboard for the matchup--everything but the four Galvanic Bombardments will come in.
Of course, Prophetic Prism and Aether Hub let you splash the aforementioned Galvanic Bombardments with very few red lands, giving the deck the single best cheap removal spell against troublesome aggressive decks that can run away with the game before you set up.
Like everyone, I'm hoping that Kaladesh Standard has more to offer than W/U Flash and B/G Delirium, and revisiting decks that fell off before this metagame was firmly established is a great way to innovate. This deck definitely has the power to compete, and if Fumigate functions as I think it can, this list solves the primary issue with the deck.
In my experience, that's usually a good sign.