Raise of hands. Have you experienced instances where dark spots appear in your dried royal icing? You spent hours flooding your cookies to perfect, and BOOM, the following day, you find grease spots all over your cookies.
The first time this happened to me, I was devastated. It was a couple of years into my home bakery, and I worked countless hours creating flag cookies only to find dark spots in the red or blue sections of my cookies. The cookies were ruined; there was no way around it. I tried painting, airbrushing, and piping over the spots, but it seemed to highlight the spots even more.
How did this happen? I searched the internet, searched blogs, and researched all I could about this phenomenon.
These dark spots are butter bleed. It happens when the butter of the cookie seeps into your royal icing. It happens more often with darker colors, and you cannot eliminate it after it occurs. The most important step I advise is to let your cookies dry out for 24 hours after you bake them before you decorate them. Allowing your cookies to fully rest after baking will help decrease the chance of any extra butter seeping into your icing.
For more information on royal icing troubleshooting, check out my Royal Icing Virtual Class. It's packed full of helpful tips, plus step-by-step instructions on making icing.