The Gibson "TV yellow" finish was achieved by tinted grain filling after an initial spray of white paint, then adding 'clear' coats over the top. The lacquers used then weren't light-fast, so quite quickly yellowed (and in the '50s their clear coats were slightly tinted to start with, not 100% clear), but often the "TV yellow" guitars were pretty white. Later they started using cream/light yellow paint and tinted clear coats when they switched to more light-fast lacquers.

Not 100% the same thing, but a similar principle. The (presumably) darker tinted grain filler will show up better against the stained wood than if you'd stained over a tinted grain filler. It may work best on a wood with a lot of decent sized grain pores, like mahogany. Ash may have almost too much depth to it if you want a level finish, though a filler only slightly darker than the body stain might work. If you look at Waz's ash body, the pronounced grain patterns are quite deep.

If you filled all those up, some of those grain lines would be almost solid filler if you then sanded it back all flat, and it could look a bit artificial. But it might not. Maybe it's worth trying to get hold of some pieces of scrap ash and trying a few different staining and filling methods and seeing what you prefer.