Divide the modeling chocolate into 6 balls. Dye it red, orange, yellow, green, purple and brown with the gel food coloring. Modeling chocolate softens with the warmth of your hands, so as you knead it, it will soften and the color will easily incorporate.
Potato: Using the brown modeling chocolate, take a small piece of modeling chocolate and shape it into a kidney bean shape. Use a sharp knife to make dimples in the potato. Use a food-safe brush to dust cocoa powder onto the surface of the potato.
Corn: Take a ½ inch piece of yellow modeling chocolate and shape it into a football shape. Use a sharp knife to first make vertical indentations in the corn, then horizontal, creating the kernels. Take an oval piece of green modeling chocolate, flatten it with your fingers and press it onto one side of the cob of corn. Repeat with a second green piece on the other side of the corn and pinch together at the base, creating a small stem. Trim off any excess green, if desired.
Tomato: Roll a small piece of red modeling chocolate into a ball. Use a sharp knife to create an indentation in the center of the ball. Take two very tiny pieces of green modeling chocolate and roll them into tiny ovals. Place them crosswise on top of the center of the tomato and press your knife into the tomato again, pressing the “stems” into the tomato.
Pumpkin: Roll a tablespoons-sized piece of orange modeling chocolate into a ball. Use the dull side of a knife blade to create vertical indentations in the sides of the pumpkin. Use a tiny piece of brown modeling chocolate for the stem. Roll an even tinier piece of green modelling chocolate into a thin sausage and shape it into a loop, creating the vine of the pumpkin. Take an extra piece of green modeling chocolate, flatten it into a triangle and place it onto the pumpkin as its leaf. You can also use the tip of your knife to create veins in the leaf, if desired.
Purple cabbage: Roll a tiny piece of purple modeling chocolate into a ball. Take another small piece and flatten it into an oval. Wrap it around one side of the ball. Repeat, wrapping it onto the other side of the ball. Continue until it begins to resemble a cabbage. If desired, trim the base off the cabbage so that it sits flat.
Carrot: Roll a piece of orange modeling chocolate into a ball, then pinch and roll one end to create a cylinder shape. Place a small piece of green modeling chocolate on top and use a sharp knife to cut the end into several pieces. Use the same knife to cut indentations into the sides of the carrot.