I prefer to use food coloring gel such as Americolor or Wilton. I prefer gels because you only need a few drops to get a vibrant rainbow of colors.
Wilton Gel Icing Colors 12ct Michaels
You can find food coloring gel online I link to it at the bottom of this post at Hobby Lobby JoAnnes Michaels or even some Wal-Marts in the craftingcake decorating section.

Americolor Food Coloring Pink Rainbow Mix For Frosting Icing Cookies Cupcakes Fondant Pastel Rainbow Food Coloring Pink Rainbow
Americolor Corp The World S Finest Food Color
75 Oz Soft Gel Paste 12 Color Student Kit 3 Americolor Corp
Wilton Gel Icing Colors 12ct Michaels
Find The Wilton Color Right Performance Color System At Michaels
Wilton Gel Icing Colors 12ct Michaels
Fourth Of July Food Coloring Set Etsy In 2022 Fourth Of July Food Food Coloring Color Set
Red Color Mist Food Color Spray 1 5 Oz Edible Spray Paint Glow Stick Party Red Food Coloring
Peacock Specialty Polyester Glitter By Recollections Cards Handmade Craft Supplies Glitter