In a medium saucepan, melt butter over medium-low heat. Remove from heat. Set aside.
In a medium bowl, combine egg yolks, sugar, and lime juice, whisking until well blended. Slowly add slightly cooled butter in 3 parts, whisking constantly. Return mixture to saucepan, and cook over medium-low heat, stirring constantly, until mixture thickens and coats the back of a spoon. Do not let mixture boil.
Pour mixture through a fine-mesh sieve into a small bowl. Add lime zest, stirring to combine. Tint mixture with food color to achieve a pleasing color.
Cover bowl with plastic wrap, and refrigerate until well chilled, approximately 4 hours.
Notes
Make-Ahead Tip: Lime curd can be made a day in advance and refrigerated until needed.
Recipe by TeaTime Magazine at https://teatimemagazine.com/poppy-seed-scones-recipe/