I'm struggling with what constitutes an active deployment point and I can't find the information in guide/rulebook.

So I get that the green points are normally the starting active deployment points, and that others can become active through mission rules. What I can't work out is if I deploy units to a yellow or red point do they become active. For example if a mission says "deploy an AT-ST to a yellow deployment point" does that yellow point become active for future status phases or is it a one off special deployment?

if a mission says "deploy an AT-ST to a yellow deployment point" it is a one off special deployment

if a mission says "the yellow deployment point is active" or "deploy an AT-ST to a yellow deployment point they are now active" then the yellow deployment points are active for future status phases

Thanks. That's somewhat disappointing but makes sense.

Depends on which side of the table you're on.