I had to make a similar call yesterday. The batted ball first bounced just inside fair territory about 2 feet short of 1B, then bounded over the double base. It looked to me like the ball bounded over the orange portion (didn't touch it, tho), and then continued into foul territory beyond 1B.
I have to set the bases up before the game. On this field, that double bag is the only one spiked down. I always put the white portion covering the entire chalk line and the rest in fair territory: the orange portion is entirely in foul territory. I spike it down so tight that it's almost impossible to move or dislodge.
This is the only way I can call a foul ball over the double bag. If the ball's entirely over the orange (sometimes a tough call), it's foul. But of course the offensive team had the 1B side dugout, and everybody thought I'd blown the call. Too bad
I'm starting to dislike that double bag. I find the foul/fair call much easier on the 3B line.