In a large dish or bowl and combine hoisin sauce, soy sauce, honey, brown sugar, five-spice powder, garlic, salt, white pepper, and red food colouring (if using).
Place the chicken thighs in the dish and make sure the chicken is well-coated in the char siu marinade. Cover and refrigerate for at least two hours. Ideally, you want to marinate for as long as possible, preferable overnight for maximum flavour.
Once you're ready to air fry the chicken, brush the air fryer basket with oil (if needed to prevent the chicken from sticking) preheat the air fryer for 3-5 minutes.
Arrange the marinated chicken in a single layer in the air fryer basket. Don't overcrowd them or overlap the chicken.
Get a small brush handy, and keep any reserved marinade.
Air fry the chicken for 10 minutes at 180°c (350F), then using tongs, flip the chicken over. Brush the chicken thighs liberally with the reserved marinade, then continue to cook for another 5 minutes. Before flipping again and brushing the marinade over the chicken again. Cook for another five minutes.
Check if the chicken is cooked - you'll also start seeing the edges begin to go a little crispy. Brush the chicken with any leftover marinade for an extra glossy, caramelised finish and air fry for just a few minutes more.
Slice the chicken, and then serve with rice and green vegetables.