In a large saucepan over low heat, melt the unsalted butter.
Once the butter is melted, add the mini marshmallows and stir continuously until they are fully melted and smooth.
Remove the saucepan from heat and stir in the vanilla extract.
Divide the melted marshmallow mixture evenly into four bowls.
Add a few drops of food coloring to each bowl to create the desired colors and mix until well combined.
In one bowl, pour in 1 ½ cups of Rice Krispies cereal and mix until evenly coated. Repeat this step for each colored bowl with the remaining cereal.
Lightly grease your 9x13 inch baking dish with non-stick spray or butter.
Take one colored mixture and press it into the bottom of the baking dish using wax paper or parchment paper to help press it down firmly.
Layer the next color on top and press it down similarly, continuing this process until all colors are layered.
Top with Easter-themed candy and optional sprinkles, pressing them down gently into the top layer.
Allow the treats to cool completely at room temperature, then cut into squares or rectangles.