why on earth is ezreal blue now

Are you talking about Pulsefire Ezreal? Frost Shot Ezreal?

Or the fact that in his new splash, the amulet he has which creates the magical bow he's using is a glowing manifestation of energy which happens to give off a blue light?

Because if it is the latter, then he's not blue. It's just the lighting from the amulet as he's using one of his abilities.

Why on earth all these why on earth-threads?

Also on topic it is the light from his bow that makes his face look blue

There was a terrible incident involving an ancient ruin with a bucket of blue paint above the door.

That bastard Shaco was seen running away from the scene giggling.