I just recently sold a suit I had. The suit they have is black other than maybe the cowl. The belt and gloves really give it away. If it was gray they would stand out considerably in comparison.From the description:
I can't really comment much on the color, as lighting and photography makes a huge difference. It doesn't appear to have the same sheen that it did on screen, but I don't know enough about how the foam rubber was painted to know if it wears off easy, or what.
They do call out the belt as being from a different suit, but seem to have missed doing so on the gauntlets. As a curious side note, I've heard that the Loony Tunes suit used the "Panther" belt, and a black version of the Sonar Suit was used by Christopher Nolan to audition actors for Batman Begins. So it looks like you could be right!
Have you emailed the Prop Store?
At best it was production made or the Looney Tunes suit. But not used in Batman Forever.
There isn't a need to contact them because they never state it was used in the film. They just say it is a display. Nothing about Kilmer ever wearing it.
My post above is not entirely fair. After I reread the listing I can see I more or less am wrong. They never state it was used.