So the general headcanon is that dragons don’t fully go from one breed to another when they use a breed change scroll. There’s usually some trait that’s left behind. Think of Scribbles with his pointed tail; many people believed (myself included) he used to be a Spiral. What if the same went for genes?
Dragons with speckle applying the metallic gene have patches of oxidized metal on their scales.
Dragons with bee/sludge applying a different gene retain their transparent wings.
Dragons with a patterned gene applying piebald keep their original patterns.
Iridescent dragons applying another gene still slightly change color in the light.
Crystal, facet, and/or glimmer dragons changing their genes still have glittery scales.
Dragons with gembond still have some of their gems stuck on their body (considering the description of Onyx Cobra ).
Capsule dragons keep their glass bellies.
Dragons who used to have runes still have glowing horns and paws.
Feel free to add some more you can think of!
Dragons with speckle applying the metallic gene have patches of oxidized metal on their scales.
Dragons with bee/sludge applying a different gene retain their transparent wings.
Dragons with a patterned gene applying piebald keep their original patterns.
Iridescent dragons applying another gene still slightly change color in the light.
Crystal, facet, and/or glimmer dragons changing their genes still have glittery scales.
Dragons with gembond still have some of their gems stuck on their body (considering the description of Onyx Cobra ).
Capsule dragons keep their glass bellies.
Dragons who used to have runes still have glowing horns and paws.
Feel free to add some more you can think of!