It appears to be another silver dragon.
If you look closely, the middle dragon does have the crest on its head; it's just viewed at an oblique angle. Look how it flows down the full length of the dragon's neck and on down the full length of its body to the tip of its tail, as it can be seen to do on the silver dragon in the D&D 3.5 Monster Manual.

It also has the swept-back horn shape shown in the Monster Manual, although the face looks unusual because we don't normally see a silver dragon from such an angle, making its characteristic round nose difficult to identify. Still, note the appearance of the wattle below its chin, again consistent with silver dragons, and the steely pupil-less orbs of its eyes, consistent with descriptions of older silver dragons (although this point is true for other metallic species). The odd markings or plates on the dragon's horns appear to be particular to this individual silver dragon or this artist's depiction of silver dragons, given the Monster Manual's description of "silvery plates on their heads".
We can see its characteristic vertical ridge which extends the full length of its tail, as we see in the other silver dragon in the picture, and it has flowing wings that are very similar to those of the other silver dragon, tipped with similar talons.
Given the artwork's appearance in Episode 6: Metallic Dragons, Arise, describing the Draakhorn whose sound calls metallic dragons, it seems likely that all dragons depicted are of some metallic type, i.e. one of the five metallic dragon types rather than some more obscure true dragon species (e.g. adamantine dragon, steel dragon etc). Given the coloration, then, it can only be a silver dragon. Given the artist's overall attention to detail in this piece, I am skeptical that it could be a brass, copper, or bronze dragon painted incorrectly.