Preheat the oven to 350°F. Line two baking sheets with parchment paper and set aside. Place the butter and sugar in the bowl of your electric mixer and beat on high until light and fluffy, 3 to 5 minutes. Turn the mixer on low and add the vanilla and salt, then slowly add the flour. Scrape the bowl and beat in the citrus zest until well combined.
Roll the dough into twenty-four 1-ounce balls (about 1 1/2 tablespoons) and arrange 12 on each cookie sheet. Bake for 12 minutes, then quickly remove from the oven and use a pestle to press a crevice in the middle of each cookie. Place the cookies back in the oven for 6 to 8 more minutes.
When the cookies are still warm, use a small spatula to lift and dunk them into a dish of sprinkles. Then place them back on the baking sheets. Cool completely before continuing.
Place the orange candy melts in a freezer zip bag and microwave 1 minute at a time, squishing in between, until the candy melts are completely smooth. Snip a tiny hole in the corner of the bag and pipe tiny kisses (or triangles) for beaks, and little 3-prong feet onto wax paper. Make more than you think you will need, because some will break.
Use the same method to melt 1/2 cup yellow (or blue) candy melts. Then pipe little wings onto wax paper that look like 3 flower petals. Don't be overly concerned with perfect beaks, feet, and wings. Move quickly for smooth flowing lines. Allow the parts to dry.
Now melt the rest of the candy melts in a medium microwave-safe bowl. Microwave 1 minute at a time, stirring in between, until smooth. For yellow chicks: Dunk one truffle at a time into the candy melts. Lift it out and place in in the center of a citrus cookie. Cover your fingerprints with the wings, then quickly add the eyes, beak, and feet before the candy melt dries. For the blue chicks: Dunk half the truffle in blue, and place in the cookie with the color line where the chick's forehead would be. Quickly add the eyes right on the line, and attach the wings. Then use the candy melt to "glue" on the beak and feet.*I found it's best to lay out all the parts for each chick before you start. That way, you have time to get everything on before the candy melt hardens.