In a Facebook conversation about making nicer-looking dehydrated citrus wheels, Jessey Qi posted a picture; a comparison of citrus wheels on a higher heat setting in a dehydrator versus a lower one. 

I think the "low and slow" ones on the bottom look much better than the burned-looking ones on top. So if your food dehydrator (or oven) offers multiple settings and you can set it below 200F/95C, then that's worth a try to make fresher-looking citrus wheels for long-lasting garnishes.