this show is pretty accurate about the CIA
1. the CIA has always been a racist organization
2. the CIA's Directorate of Operations
exclusively recruits sociopaths to become CIA officers.
3. Teddy was racist and a sociopath- and he treated Oso differently than Franklin but race wasn't the reason
Teddy recruited and "ran" Franklin as an asset / agent. Officers care about assets only in context of the asset's usefulness to the mission- train mentor manipulate/ provide motivation and logistical support.
Oso is a soldier - initially he was one of the Nicaraguan rebel's liaisons to the CIA to keep the money and weapons flowing to the rebels,
so Teddy treated him as an officer from a US ally, pretty much the same as Avi.
Later Teddy was officially cut loose but secretly tasked to continue the mission off books / black. Thats when Teddy recruited Oso to also start working for him and CIA as an operator under Teddy's direction to support the mission by doing counter intelligence, leg work, or wet work as needed
Thats when Teddy started treating Oso like a junior officer giving him operational information and context a little beyond need to know.