The real issue is that stereotypes apply to classes only and not to arrows.
So something like "ArrowColor<<greenColor>> Green" should apply to arrows that are stereotyped to <<greenColor>>, and right now you cannot define stereotype arrows.
We could imagine that "ArrowColor<<greenColor>> Green" would apply if one of the classes connected by the arrow would have <<greenColor>> stereotype.
Is this what you are expecting ?
Putting it differently, in the following example, are you expecting the arrow to be drawn in red ?
@startuml
skinparam class {
ArrowColor Green
ArrowColor<<stereo1>> Red
}
class foo1 <<stereo1>>
class foo2 <<stereo1>>
foo1 --> foo2
@enduml