I’ve got a few for you.
Federal Signal Hammertone Silver/Grey
Found on all grey horns manufactured by Federal Signal (e.g. Simplex 4040/41, Federal Signal 350/450, etc.)
Federal Signal Aluminum Finish
A rather uncommon finish, only seen on Federal Signal’s products so far. Basically bare aluminum, which is likely what the 4" horns are made of
IBM/Simplex Wrinkle Grey & Red
Found on fire alarm control panels, and Simplex 4045-12 chimes (grey only), popular finish c.1960s-1970s
Faraday/Simplex Smooth Red Finish
Found on fire alarm horns manufactured by Faraday (e.g. Simplex 4050/51, Faraday 5410, 5420, 5430, etc.)
Faraday/Simplex Smooth Metallic Grey/Beige Finish
Ditto, but grey/beige variants, most-often for non-fire alarm use
Faraday/Simplex Spartex Red/Grey/White
Textured finish found on mid/late 70s → early 80s horns manufactured by Faraday (e.g. Simplex 2901-9833/34, Faraday 5970 (grey), etc. White seems to be super rare)
Photos:
OSFA
Old EBay listings
Spartex White 4050 Post: GothYoda's Collection