Line a baking sheet or large plate with parchment paper.
Place 6 ounces white chocolate chips into a microwave-safe bowl. Place 6 ounces pink candy melts, 6 ounces light blue candy melts, and 6 ounces yellow candy melts into separate microwave-safe bowls.
Add 1/2 teaspoon vegetable oil to each bowl of melted candy, using a total of 2 teaspoons vegetable oil.
Microwave each bowl in 15 to 20-second intervals, stirring after each interval, until the chocolate and candy melts are smooth and completely melted.
Using a fork, dip each of the 16 Oreo cookies into one of the melted candy coatings, allowing any excess coating to drip back into the bowl.
Place the coated cookies onto the prepared baking sheet. Alternate between the white chocolate, pink, blue, and yellow coatings until all 16 cookies are covered.
Refrigerate the cookies for at least 1 hour, or until the coating is completely set.
Transfer any remaining melted white chocolate and candy melts into separate piping bags or zip-top bags with a small corner snipped off.
Drizzle the remaining melted coatings over the chilled cookies and immediately decorate with spring pastel sprinkles.
Refrigerate for an additional 15 minutes, or until the drizzle has hardened. Serve and enjoy.