Hey everyone! If i make drop flowers w/ dark blue royal icing, are they going to bleed onto the white buttercream when I attach them to the cake?

As long as the flowers are completely dry they shouldn't fade onto the buttercream.

When I use royal icing I let it dry a whole 24 hours before putting a darker color on it. Otherwise it will bleed. Lighter colors on lighter colors are usually ok after about an hour.