Preheat your 5- or 6-quart air fryer to 250°F for 3 minutes.
Cut the orange and purple carrots, parsnips, and beet in half lengthways.
Using a mandoline or V-slicer, slice the veggies, cut-side down, into very thin (2mm-thick) slices.
Taking care, pull out the air-fryer pan and basket.
Place purple carrot and beetroot slices in the basket.
Slide the pan and basket back into the appliance.
Keep the temperature set at 250°F and set the timer for 30 minutes.
Cook, stirring halfway through the cooking time and separating the slices until the veggies are crisp.
Transfer the purple carrot crisps to a tray and cover to keep warm.
Cook the beet crisps for another 5 minutes and transfer to the tray with the purple carrot crisps.
Spray the crisps with cooking spray and sprinkle with salt flakes.
Cool.
Repeat the cooking process with parsnip slices, then orange carrot slices.
Cook at the same temperature and for 25 minutes each.
Add them to the tray with the purple carrot and beet crisps.
Spray with cooking spray and sprinkle with more salt flakes or one of the seasoning variations below.