Spot in with which came first! (@henddraig)
But I myself (for what little that’s worth!) would say rather that llyffant is a “froad”, [in a similar way to the way malwoden can cover snail and slug, (IE a slail or a snug) or madarch can cover mushroom and toadstool (that is to say, a toadroom or a mushtool 
) and that though in a lot of minds (including my father’s), llyffant has become restricted to toad and the newer ‘broga’ works for frog, it is just as good and right and proper to think of a toad as a “dark frog” as it is to think of a frog as a “yellow toad”!
Or, as I say the third option of a “black froad” and “yellow froad”! Cc