Key limes are yellow, and that is the colour of an authentic Key lime pie, which is nothing more than a custard of Key lime juice, sweetened condensed milk and egg yolks in a cracker crust, then topped with meringue or whipped cream.
Neither of these is actually true, as would have been clear to anyone who perused the entire news release or dissected the colour-coded key to the map.
At key moments, for example, Mr Scorsese floods the screen with colour filters to provide a powerful visual correlate of what his characters are feeling.