I don't see redundancy here. That might be the case if "darkness" were only considered as something (literally) seen. However, it is also a quality, something which is (intuitively) felt. And it is this sense which changes in the poem, and gives it depth and surprise.
The first of the two is far better. I would suggest two changes, but they alter (deepen I would say) the poem in ways the author may not wish, so I'll refrain.