Game Boy Pocket Rainbow Case

[fredJ]

I bought a bunch of game boy consoles from Japan. One of them had this case , the japanese text says "Rainbow Case" , I think.
I have no idea who made it but is very professional, as you can see the text is in white which is I don't think any other GB Pocket console has.
The inside is from a normal Nintendo PCB.

Any ideas? I plan on asking 25$ for it. But I was thinking maybe it is something super-rare...