I should have mentioned that I am trying your Affinity Photo Beta. When I mouse over the tool it shows as Flood Select Tool just bellow the Selection Brush Tool. It looks like a Magic Wand.
I am an angry ex CoralDraw 11 user. Many years ago they thought Mac was going nowhere so they dropped all their Mac users like a hot potato. The person or persons who made that decision are today kicking themselves in the seat every morning before their first cup of coffee. We have somehow managed to keep Coral 11 alive all this time but it has finally gotten to the point where it needs to be taken to the cemetery for a tearful goodbye and bury it. If you could somehow get the attention of the Coral Mac users you will be mending a lot of broken hearts. I found Affinity on one of the Coral "begging for Mac version" forums where a few users mentioned Affinity.