I would, personally, make the whole thing metaphor and kick out the similes. There are places where you explain the similes and I think that it slows it down and busts the rhythm you’re setting with the repetition (which I like very much by the way) and if you have to explain the image, then you need a better image. (It’s the "show, don’t tell" thing.) Find ways to cut down on the word "as". For example: At periods I’m pure as white. Most lines where you have the as-word-as construction, the first as is idiomatic and isn’t grammatically necessary. Use it to maintain a rhythm, but not just because you’re used to it being there.

I would also keep the "I am" consistent throughout the poem, rather than use I’m. The reason is that "am" is such an important part of it, that cutting it out kind of hurts. It also doesn’t hurt that "I am," when said aloud, is a light stress – heavy stress when you settle into the poem. This happens because "at periods" is iambic. It’s a very soothing kind of foot to have. I’m is a heavy stress, but it’s not bad because then you’ve got an iamb followed by an anapest. (at PER-i-ods I’M) as opposed to (at PER-i-ODS i AM). Because you’ve got such a great couple of beginning feet (whatever you choose) you’ve got a great flow to start with. It’s why lines like "a stick ductile material" interrupt you. The flow established rhythm should break because the line is really, really important. Like the "But I know" line.

One issue I really did have is that I didn’t get the logical flow of what any of that stuff really had to do with twilight. Aside from "weird" and "orange," none of the other images had much link with the idea of twilight. But that’s just me. I don’t know how tied you are to the word twilight, but you can try changing it to something like "I am Joe / the period of Pisces." It doesn’t take much of a stretch to tie the qualities you’re listing with the idea of what kind of a person a Pisces is. That’s just an example.