Blsck in a matte finish.

What room is this going to hang in? Or will it be outside? Could make a difference in the colour you choose to showcase it.

Probably a red might work the best as a contrasting colour but all depends how dramatic you wish to be.

It hangs in a alcove ( I guess). It's the entrance to my husbands office. You see the wall and you turn into his office. It's more a feature wall. The entrance to the house is painted a green/gray and office is gray. The wall is painted purple now so I'm not afraid of color but it looks horrible against it.

If you want the wall to be part of the art piece then in my opinion you should paint it the same yellow as the lettering.....if you want a background color that will look good with the rest of your house I think you might need to choose a neutral rather than a color. Can you show us a picture of the sign? Even how it looks hanging on the wall (doesn't matter if it is purple).