So, I got a GBA today, since I lost mine forever ago, along with my GBASP, and decided to pop in Red version.
I was giving Oak his parcel thing, and he was like, "OH, it's my CUSTOM ball I ordered."

And I'm not sure if this is just me being dumb, but is this a hint to the customization we can do with Pokeballs in Gen 4? Picture not related.