
Hi Sin
A few suggestions to accompany your culling regime:
L1 -- inside isn't necessary, unless you're going to develop further the contrast between essence and appearance.
L2 -- coming and going is an expression that could, if you're concerned primarily with cutting stuff out, be replaced by passage [rather than passing, which tends to emphasize the going].
L3 -- I'm not sure how to interpret the original line (each season forth/each promise/each color), though if the last of those applies, you could retain the idea by replacing promises with a promise, to imply that each season is characterised by a distinct flavour characterized by colour. Although brought forth may have some rhetorical value in the context, forth is not essential to the meaning.
L4-5 -- I saw from scattered eyes; I think through would be more appropriate than from. Although I'm not a huge fan of inversion, in this case it might be preferable to say [something like] through scattered eyes, I saw/watched...
As each faded toward the next is [to my untamed ear] a bit awkward. I wonder if you'd consider [something like] (I watched/saw) each fade and flourish (where each takes the form of adjective, modifying 'fade' and 'flourish', rather than pronoun referring back to season or color).
I know flourish might not be an ideal way to describe the 'coming' of every season, though a similar argument could be made regarding fade. Anyway, I think your point is that one 'dies away' as the next 'comes to life' [as inferred by promise of color].
The last line doesn't strictly need to one, although without that, it lacks a satisfactory note of finality, if only through the reduced syllable count. Perhaps an alternative for merged would redeem that loss -- maybe [something like] coalesced?
If that isn't much help, please bear in mind that it's late, and I'm fading rapidly into the contradiction of terms that calls itself 'tomorrow' [because today is here already]

Hi Laura, thanks so much for your detailed suggestions, it really is helpful. I'll post a third version with some of your suggestions. Again, thank you for taking the time to critique this one;)

as each faded within the next
I like the idea, as expressed in this version -- the seasons (represented by their colours) without distinct boundaries, each 'dying' within the life of the next.
I wonder if within me might be a more compelling last line? It would suggest a tangible connection between narrator and subject (seasons, as metaphor), and provide a a conclusion to balance the introduction, both of which would directly address the narrator as (literal) subject.
That's just my take on it. Fascinating to see this progressively stripped down to its flesh, not that I'm admitting to voyeurism

Laura, yep it's pretty stripped down, lol. I agree that there needs to be more of a connection (clear-cut metaphor), but I'm not sure yet how I'm going to revise it. Thanks again for the suggestions:)