Unfortunately, I've just bought a new API ammonia test, but I might try the Nutrafin one next time. Apparently that goes clear/pale pink/pink/red. I think it might be easier to see 'clear v pink' as opposed to 'greeny-yellow v yellowy-green'.
The Nutrafin ammo test is also yellow for 0ppm, IIRC. The AquaOne ammo test is clear for 0, however their nitrite is yellow for 0. Why can't a manufacturer make a set of 3 tests where they are all clear on 0ppm?