In a medium mixing bowl, stir together the refried beans and taco seasoning until well combined.
Spread the bean mixture in an even layer across the bottom of a 9-inch shallow glass pie plate or round serving platter.
Carefully spread 1/2 cup of the sour cream over the bean layer, followed by an even layer of guacamole, and then the salsa.
Distribute the shredded cheddar cheese in a 1-inch wide ring around the outer edge of the dish to create a festive orange border.
Transfer the remaining 1/2 cup of sour cream into a small plastic resealable bag and snip off a tiny piece of one corner to create a piping tip.
Starting from the center of the dip, pipe four or five concentric circles of sour cream over the salsa layer.
Take a toothpick or the tip of a knife and draw straight lines from the innermost circle out toward the cheese border at regular intervals to create a spider web effect.
Arrange the sliced black olives on top of the web; place two slices together or use one slice with small slivers to mimic the shape of spiders.
Garnish the orange cheese border with the diced tomatoes and green onions for extra color and texture.
Serve immediately at room temperature or chill for up to 2 hours. Serve with blue corn tortilla chips for a dark, spooky contrast.