ODSTs on The Ark Lore Question

I am planning on writing a short story (and possible fan film) revolving around a veteran of the 7th Shock Troops Battalion living life post-war. I want it to start out on The Ark as a sort of flash back, the character being one of the ODSTs that we see in H3. My question is this: what are the colors on the ODSTs arms (white and red) indicative of? Speciality? Squad? Is there any lore I could read on the 7th STB in general to get a better idea of who they are and what their structure is like? Any help is appreciated.

Dug up an old thread with the different shoulder colors for ODSTs: What different colors mean for ODSTs

Looks to be a specialty designation.

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> Dug up an old thread with the different shoulder colors for ODSTs: What different colors mean for ODSTsLooks to be a specialty designation.

That is OLD old, but surprisingly not inaccurate if it has sources like those.

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Name the protagonist Farthead plz