The first answer is correct at that moment: The shore is a continuing obstruction
and rule 19.2(b,c) applies.
In accordance with rule 12, Green must keep clear of Blue who is clear ahead.
Under rule 10, Blue (port
tack) must keep clear of Red (starboard tack) boat but Red (the outside boat)
must give Green (the inside boat) room in accordance with rule
19.2(b). Red will also have to give Green room, if Green moves away from
the shore to overtake Blue. (If Red establishes an outside overlap on Blue,
Red will also have to give room to Blue. See also Case
30).