https://www.tastingtable.com/1547795/avoid-liquid-food-coloring-dyeing-buttercream/
If you want to dye buttercream with liquid food coloring, tread lightly. Being aware of liquid food coloring's power can save your buttercream from disaster.
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https://www.chowhound.com/1601885/gel-vs-liquid-food-coloring-best-cookies/
It's best to use liquid food coloring when you want a light pastel cookie, and gel for when you want a treat that is more vibrant and colorful.
liquid food coloringgelvsbest