I went in with Divine Protector. The colors are still correct for that weapon. It is also the mana needed to use the weapon. But the weapon ability matches the weapon pictured, Flammifer.
Earlier in the week my Runic Blade was changed into Elder Bow. It was the same issue, the Runic Blade colors filled it, but used the Elder Bow ability.
Can you please PM or let me know the name of the opponents you fought so I check the logs of this for you?
And to clarify, I understand your issue is that you edited an Arena team with a Weapon, but when the battle loaded the game replaced the weapon with something else. This happened with Divine Protector > Flammifer and Runic Blade > Elder bow.