Wipe room-temperature hard-cooked or blown-out white eggs with distilled white vinegar; dry thoroughly. Dye gray following egg-dye manufacturer's instructions. Remove from dye bath; gently dab with a paper towel and let dry completely. Combine with undyed hard-cooked or blown-out brown eggs in various natural shades.
Place a self-adhesive stencil onto an egg, carefully pressing it onto shell to ensure there are no gaps. Dip a small foam dabber into white craft paint, making sure not to oversaturate (so extra paint won't leak). Push tip of dabber over stencil cutouts. Remove stencil immediately, before paint dries. Rinse stencil while paint is still wet.
Let pattern stenciled onto egg dry, then repeat until motif is to your liking. Repeat with more stencils and eggs.