They're not dying. They are shedding their older foliage. It's normal.
It's called 'Flagging'.
Mike

Arborvitaes turning orange is not normal. Not at all. They will brown out some on the interior and drop some needles this time of year, but what the OP describes sounds very serious.

bot meant.. INTERIOR shedding is normal ... what he said ...

exterior.. next years buds.. should not yellow or brown.. what she said ...

they are conifers.. they are trees.. but they are not shrubs .... follow rules consistent with either.. but not as shrubs ...

a pic will get you a precise answer.. unlike the two guesses above ...

ken

I assumed interior. Every year at this time we get the same question.
Mike

Holy cow! Did I contradict Botann? After so many years, I should know better! Sorry, Mike, I think we were visualizing two different things.

Problems with root rot on very frequently planted Thuja occidentalis 'Smaragd' are widespread and chronic. Otherwise, heavy summer mite buildups are sometimes seen affecting the coloring of these also. Arborvitaes, box and mahonias may also go all or partly orange at some times - I just had a couple Mahonias go partly orange recently, at the same time that the weather became cooler - maybe this is a nutrient deficiency that shows when soils are less warm. Since these three types of shrubs do this so often there is probably information available saying what is happening - I may have seen it talked about in The American Boxwood Society boxwood handbook for instance. When I see it the affected shrubs look like the site conditions are definitely less than optimal, with growth not being full and healthy looking in other ways in addition to the orange discoloration.