How do you unlock the non-prototype Stealth Camouflage?
Solution 1:
You need to complete the Yellow Side Ops to retrieve the AI Pod.
After completing both this and mission 43 (Shining Lights), you should be able to trigger Huey's ending.
Go ahead and complete random side-ops -- eventually Miller should interrupt you and tell you to get back to base, where Huey's final scene will play out.