I actually meant when using the original stickers
(i have some here) if you match that yellow it will look better than if you dont, my years as a painter & paint mixer taught me that looking correct is better than "being" correct.
Manufacturers never produced one exact shade, each colour listed for vehicles always had 2 to 5 shade variations simply because the batches varied in the factory.
Its extremely unlikely that BSA tanks in that yellow were all the same shade variant.
Another big problem the industry had was that the tank paint will fade (as all paint does) at a different rate to the vinyl sticker
so they wont match after 6months in ultra violet exposure anyway.
Next huge problem is that yellow pigmented paint has awfull coverage often its heavily influenced by the primer colour & number of coats applied, i & others in the trade always used primer of a similar colour to finish colour.
If you have vinyl tank decals
made like on victors, i suggest you ask for (slightly more expensive) laminated finish, they fade less & you dont need to lacquer over everything as you often get problems putting paint over vinyl.
Personally i reckon the paint might have been bought in as correct but transparency problems & shade variation ruined the match as with the famous red Citroen BX cars with the plastic bonnets, they never got them to match in production.