use gel colors when dying royal icing to prevent the addition of excess liquid. It’s best to add color after the royal has been whipped. You can add the color before you whip the royal, however the color will lighten with the introduction of air during the whipping process.
For dark colors, additional sugar should be added to make the royal more firm. It’s also helpful to cover the royal with a wet cloth and let it rest. The color will intensify after roughly two hours – try leaving it overnight