I have a 1951 Riley RMB (my first car!) which is nearing the end of its restoration (took it off the road in 1975 to replace the roof covering...a 3 or 4 week job....ahem!). Most of these had black roofs, but other colours were optional, and mine is going to have a maroon roof.
Perhaps I should explain. The Riley RMB is a saloon car, which had a fabric roof covering, same material as a cabriolet. This roof covering is nailed onto the wooden framework around which the metal panels of the body are nailed and welded (yes, the wood framework does get burnt....what a daft way to build a car body). The nails for the roof material are covered by an aluminium moulding, which is also (blind) nailed to the roof; so this sealant is needed to seal between the aluminium & the roof material; vital as otherwise, water gets to the nails; rusts them and rots the wood. You can just see some of the holes in the roof metal for the nails.
The problem is, finding a permanent weatherproof flexible sealant that is at least close in colour to that of the new roof covering. Nearest found so far have been "Bright red" and "Brick red", which aren't close enough. So, knowing the wide range of employment and expertise on this forum, I wonder if anyone can suggest a suitable product and supplier.