It can be that some airfields use differing colours of hi-vis to identify particular roles to assist in identifying in an emergency situation.
As you say you intend to be active at a number of place it might be tedious but best to simply contact them explaining your needs and asking their requirements, an e-mail bcc'd to each perhaps?
Might cause consternation if a small airfield suddenly had a dozen fire chiefs or Operations Staff running around one day
In my experience the standard yellow tends to be the "normal" hi-vis with the orange/red used to easily identify those with a particular function/role in an emergency situation.