I found a fix if you have blotchy royal icing on your cookies. Put the cookie in the oven (turned off) and leave the oven light on. After a few hours, your whole cookie will be the same color. It will turn a darker color (the color of the blotches), but at least it’s all the same color. This is for if your blotches are due to butter bleed. It just barely warms the cookie enough to bleed the butter to the whole surface. I tried it yesterday, it works!