MTG Salvation

So my friend has the new Arcane Wizardry deck from Commander 2017 which is Blue, Black and Red. I have the Feline Ferocity deck which is White and Green so neither of the decks share a color identity. My friend cast Spelltwine and took one of my Green spells from my grave yard, Harmonize, and wanted to draw three cards. But since Spelltwine specifically says that you can "cast" the target cards, I thought that he would not be able to cast it as it doesn't share a color with his commander. Can someone please help?

Yes, they can. Colour identity restricts what can be put into the deck, not what can actually be cast. (As long as they can somehow get around paying the cost)

Quote from Eruyaean »

Yes, they can. Colour identity restricts what can be put into the deck, not what can actually be cast. (As long as they can somehow get around paying the cost)

You don't even need to get around paying the cost, since cards like Gilded Lotus, City of Brass, etc. can generate mana outside your color identity.

Oh right, The "Mana outside the colour identity becomes colorless" Thing hasn't been a thing for almost two years... I forgot.

Also also, Spelltwine says "without paying their mana costs", so even though you can produce mana of colors outside your commander's color identity, it's moot in this case.