Tamiya has released a “Panel Line Accent” line with 4 colors: Black, Brown, Gray and Dark Brown. They are an enamel-based wash, so it is smelly and it could attack bare plastic, so test it on a scrap piece (a runner or extra part) first.
The panel line accent is packaged in the same kind of bottle than the Tamiya Glue down to the small and thin applicator brush, which comes in very handy when applying it to a recessed panel line.
In this review I applied 3 “spots” of panel accent line to an unpainted piece (leftover) from and Eduard model and it did not damage that plastic. Not only that, but 3 applications were enough to see all the panel lines completely covered. The wash just flows on its own along the whole panel line.
Then I decided to try this product on a Bf-109F-4 which had a coat of Future on top of the decals. You can see the before/after application. They speak by themselves. Very restrained, yet clear surface detailed popped out due to the application of this wash.