Dead Cruiser said
Everyone has a bit of every color, but one's current behavior and philosophy are generally what dictate their colors. See: Planeswalkers that have been different colors.Blue = Artifacts fo sho though. A spell that summoned craploads of swords would be hella Blue. Reminder that colored artifacts were introduced as the gimmick of the Primary-Blue shard of Alara.
But that's merely trying to ascribe a colour by the effect, rather than a colour by the 'why'. Beyond that, you're assuming that UBW works as 'summon loads of artefacts' or even
as an artefact, then saying that it's Blue--when the actual effect could be something more like grindclock, where you just tap it and check counters to see what the hell it does.
On top of that, Unlimited Blade Works itself exists because of Avalon, which is utterly White, and even then only because Archer/Emiya Shirou basically defines himself around saving people. Simply using it, as the Reality Marble or as normal projection, damages a human body--oh, hi, Black. Even though Archer plans, he hasn't removed the tendency to throw himself in harm's way and just take the more direct option; plus all the fucking blacksmith connotations and smog. As for Green? Contract with the world to reduce the pressure on the destruction of UBW--and he's a Counter Guardian, so inherently part of the natural order.
Inside Unlimited Blade Works, it isn't the same as being inside a Blue artefact-spamming Land or something. A Reality Marble is the projection of a character's soul, essentially, onto the external environment: the effect might say one thing but the actual reasoning would be completely different. Colourless incomprehensibility it is. Not a mere blue because artefacts.
If I had to turn it into a Magic card--and note that this is not the same as how it will appear in the roleplay, if used--it would either be Black/White or Blue/White. It would not be mono-colour Blue.
