Butter (or line with parchment paper) a 9 x 13 or similar casserole dish.
In a large pot, melt butter over medium-low heat until just melted.
[mv_schema_meta name=""]Turn the heat off and stir in the marshmallows. The residual heat from the melted butter should be enough to melt them, but if it is not, turn it back on low until the marshmallows are smooth.
Remove the pot from the stove. Stir cereal and cotton candy in with the marshmallows until everything is coated and combined. Some of the cotton candy will melt, some won’t.
Quickly spread into prepared pan.
Let cool and cut the treats into twelve bars.
In two separate bowls, melt the blue discs and the white discs.
Press the bars into the white coating. Drizzle blue on top of the white.
Top with sprinkles while the candy melts are still wet. Let candy topping harden, then serve.