Black Tie

Black tie refers to the formality of the event and the high level of hosting being provided and implies that the guests should dress accordingly. It has nothing to do with the color of their attire. A tuxedo is appropriate for an event that is designated as Black Tie formal.

A tuxedo doesn’t have to be black to be black tie appropriate. Navy is also fine.

A tuxedo of any color is appropriate for black tie. Black tie means formal not that guests need to wear a certain color.

View Quoted Comment This exactly. OP, are you having butler-passed apps, a multi-course plated meal, top-shelf liquor, valet parking, a live band?

Black tie is a dress code for weddings if you put that a lot of people will be in tux and formal long dresses. It is passed apps and valet parking.

View Quoted Comment Yes, we having all that for cocktail hour

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The entire event needs to have those things. As others have already said, "black tie" refers to the formality of the event and the level of hosting; it does not mean that only black tuxes are worn. A black tie reception should begin no earlier than 6 p.m., have white glove service (this means that guests do not lift a finger for anything - there are dedicated servers to care for their every need), valet parking, open top shelf bar for the full event, live band, and a multi-course plated dinner. We had a black tie wedding and paid about $315 per person just for the catering.

You respond with yes, that’s the attire you requested.

Omg tell them to re read the invitation lol

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How can you have a multi-course plated meal for cocktail hour?

You don't have to have black for black tie technically. In my area you'd be looked at funny for having a blue tux but I digress.
You can say yes if he can't find a black one. It makes the point you prefer black but he doesn't have to wear black as he's appropriately dressed.

I’d say “sure, as long as it is a tux”

You say "awesome, sounds perfect!"

Not sure what the issue is....

She likely means a navy blue tux which is a style that is becoming popular and trendy, in case you were thinking she meant a powder blue tux out of the 90’s.

A blue tux is definitely appropriate for a black tie wedding. You can’t delegate what colors people wear.

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Why? A blue tux is completely appropriate for a black tie wedding. Black tie is a level of hosting, not the color people are supposed to wear.

A blue tux is 100% fine for a black tie wedding so I don’t understand the issue here at all.

Unless your servers/butlers will be wearing a blue tux, and you don’t want him to be confused with the staff, it’s perfectly fine for him to wear a blue tux.