Food coloring. This is my favorite recipe for BBQ pork, the method also works quite nicely for ribs.

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Title: Cantonese Barbecue Pork
Categories: Chinese, Pork, Ceideburg 2
Yield: 1 servings
3 To 3 1/2 pounds pork butt,
-shoulder or tenderloin
4 tb Soy sauce
5 tb Sugar
3 tb Honey
2 tb Hoisin sauce
1 tb Grated fresh ginger
1 tb Shao Hsing rice wine or dry
-sherry
1 1/2 ts Salt
Mustard Dip (recipe follows)
3 tb Toasted sesame seeds
Think of these sweet, glazed strips of roast pork as the ham of Asia.
Both Chinese and Southeast Asian cooks serve cha siu as a main dish,
or as a meat addition or a delicious garnish in many stir-fry
mixtures, soups, noodle dishes and fried rice. Most Chinese cooks
purchase their cha siu already prepared at a roasting shop
(delicatessen). However, it is very easy to make at home, and the
results are not as garishly red as some commercial versions made with
food coloring.

Remove and discard the excess fat from the pork. Cut pork lengthwise
(with the grain) into 2-inch wide strips 5 to 6 inches long. Put into
a large bowl.

Combine soy sauces, sugar, honey, hoisin, ginger, wine and salt. Pour
over meat and rub it in well. Cover and marinate in the refrigerator
at least overnight or for up to 3 days, turning several times.

Preheat the oven to 350F.

Place the pork strips on a broiler pan lined with foil. Roast for 30
minutes, turning once halfway through. Increase the heat to 425F and
roast for 10 minutes longer. Let cool before slicing.

To serve, cut across the grain into 1/4-inch thick slices. Serve with
mustard and sesame seeds for dipping.

MUSTARD DIP:

Mix together 2 tablespoons Colman's mustard, 2 tablespoons water,
pinch of salt, pinch of sugar and a few drops of oil.

Joyce Jue, San Francisco Chronicle, 1/8/92.