I'm almost embarrassed to admit, I found an online image of the colors of the sky through the day, pasted it into excel, and then capture 160+ rgb values for the sunset. It was a tedious process, but no math got it right.
I set all those values (and a warmer and cooler set) in the script and then pass in the desired duration. Most nights we have a 45 minute sunset play out across 6 total lights. Three sets of values, so the bulbs don't match.
Starts as soft white ending in the darkest twilight blue my bulbs can provide. We remark on it regularly and I think it's helped ease us into the right frame of mind for sleep.