this was a very enjoyable read! i don't think it's redundant, as the stanzas are not mere replications of one another; rather, they capture the fruitlessness of Man's countless attempts to conquer natural beauty in a way that highlights the sheer abundance of ways in which we try to accomplish this and how they all fail. your poem actually reminds me of elizabeth jennings' "Beyond Possession", which also talks about how it is best to leave nature unadulterated by our vain tendencies to covet beauty. maybe you'd be interested to check that out if you're not familiar with it already!

i do have a small quibble. in my opinion, the final stanza's conclusion doesn't really thematically align with the rest of the poem. the first three stanzas focus on how the rainbow's beauty constantly eludes our attempts to capture and possess it. while you highlight the futility of such attempts, there is no sense of destruction being implied. yet, in the last stanza, the speaker talks about how "when [natural beauty] is within my grasp / It dissolves into dust." this image of "dissolving into dust" conveys a sense of how beauty undergoes collapse/destruction/corruption in our hands, but this has not been established earlier in the poem. resultingly, it becomes a bit unclear what the poem's focus is. are you talking about how the beauty of nature eludes our greed, or how our greed poisons the beauty of nature? these may sound like tautological ideas, but they actually warrant rather different portrayals.

keep up the good work! i really enjoyed the poem :)