Some apple varieties are less of a draw for maggot flies. Wolf River jumps immediately to mind. I might have included Winthrop Greening as such in past years, a greenish-yellow Maine heirloom ... but this season, with relatively few apples throughout the orchard, any and every orb emitting apple essence seemed to be fair game. I even found a few larvae in the Golden Russets which is very unusual.
As regards the sticky spheres, Ron Prokopy at UMass did explore which was the right color to best draw AMF attention. Red won hands down over green and clear. Yet equally involved as a "dark silhouette" at this stage were odor essence, position in the tree, and proximity to other fruit. The decision to lay an egg in a particular apple came down to fruit size, color, penetrability, sugar content, and water content. Yellow panels proved a draw to immature flies, the thinking being that infrared reflection was similar to that of bird poop, which young AMF feed on.
Lost Nation OrchardZone 4b in New Hampshire