There's intense lime flavor in every bite of this citrusy frosting.
The thawed frozen limeade concentrate gives the frosting intense lime flavor. Be sure to thaw it completely before adding it to the mixer bowl.
Using stand mixer fitted with whisk attachment, whip butter on medium-high speed until smooth, about 20 seconds. Add sugar and salt; reduce speed to medium-low and whip until most of sugar is moistened, about 45 seconds. Scrape down bowl, add limeade concentrate and vanilla, and mix on medium-low speed until incorporated, about 45 seconds. Increase speed to medium-high; whip until light and fluffy, about 4 minutes, scraping down bowl as needed. Add green and yellow food coloring and mix until combined.