Here is a screenshot of my exact settings. https://share.icloud.com/photos/0JqR40SehiTKKecdCQB5NXZmg

I’m not sure on the RGB hex values. However F.lux determines the color by a kelvin rating. I’ve shared the kelvin ratings for F.lux below.

Ember: 1200K Candle: 1900K Warm Incandescent: 2300K Incandescent: 2700K Halogen: 3400K Fluorescent: 4200K Sunlight: 5500K

I’ve found the color is closest to candle light when using the color filter plus night shift.

The ideal solution is a nightshift enhancer that matches the kelvin rating of f.lux but I have not found any tweak that is comparable with iOS 12/A12 that achieves the desired affect.