Your perfect pitch ability is not effected by French Horn and Piano being in different tuning. Each tone has the same flavour regardless of what the note is called. Perfect pitch isn't about memory anyway, it's a different way of hearing every note, like colour hearing.
If you call the colour blue "yellow" you still see the colour blue.
But it is very difficult to develop perfect pitch so most of us see in black and white
It's no trouble though, relative pitch is far more useful and you really don't need much else if you can do this.
I play a lot of games blending notes together and letting my ear distinguish each one. Little things like that help.