Still thinking that red, yellow, and probably grey are colours that are out-of-stock in the old style. Less certain on the grey, since those are often not customized. Possibly the resorts just keep some uncustomized grey on hand, so that one could vary by resort. Guessing about the grey aside, there's been no evidence that a specific resort or resort category makes any difference at all.
Still just a theory, but so far I haven't seen any data points to contradict.
As of this week, all reported orders including red have received new bands. Any reported orders of blue, green, purple, pink, and/or orange *without* red included have received old style bands.
We have one report way back of a new standalone yellow band, and nobody has since reported receiving an old style yellow band. The only report of yellow I've seen since then also had a red band in the order, so no additional data there.
Keep those colour data points coming!