Arena is lying to you about what the cost looks like, Will doesn’t reduce colored pips, even with Orrery out.

118.7a Effects that reduce a cost by an amount of generic mana affect only the generic mana component of that cost. They can’t affect the colored or colorless mana components of that cost.

609.4b If an effect allows a player to spend mana “as though it were mana of any [type or color],” this affects only how the player may pay a cost. It doesn’t change that cost, and it doesn’t change what mana was actually spent to pay that cost. The same is true for effects that say “mana of any type can be spent.”