If the claim is that "all ravens are black", then it's true to say that every new raven I see that's black supports the claim. If that's true then yes, by equivalence it's also true to say that if I see a non-raven that's not black this also supports the claim.

However the fact that they both support the claim, does not mean that they provide equal support.

Consider what it would take to be certain that all ravens are black, one of the following needs to occur.
i) ravens need to be defined as being black
ii) we need to see all the ravens and all of them need to be black
iii) we need to see all the non-black objects, none of them can be ravens and I need to know ravens exist (I need to state that ravens exist here otherwise you could prove that all unicorns are pink by observing that all non-pink objects are not unicorns).

Case i is trivial. Case ii requires the observation of far fewer objects than case iii. Therefore one observation of a black raven supports the claim more than the observation of a non-black non-raven. The degree that an observation of a non-black non-raven supports the claim depends on how many non-black objects there are. If there are a finite number of non-black objects, then an observation of a non-black non-raven would support the claim some non zero amount. If you claim there are an infinite amount of non-black objects then the support for the claim from observing a non-black non-raven would be infinitely small. In either case, it would be hard to imagine any number of observations of non-black non-ravens changing your stance on whether all ravens are black.