You use the avatar editor in Roblox, not a special “skin ID” field, to change a character’s skin tone or custom look. In Roblox’s help docs, skin color is changed from Avatar > Head & Body > Skin Tone on web, or Avatar > Customize > Body > Skin on mobile.

How to do it

  1. Open Avatar.
  2. Go to Head & Body or Body.
  3. Select Skin Tone or Skin.
  4. Tap the color you want.
  5. If you want different colors for individual body parts, choose Advanced and edit each part separately.

About “custom skin id”

If by “custom skin id” you mean a Roblox item or clothing code, Roblox supports adding item IDs through the avatar editor’s Advanced options, where you can input an Asset ID from an item link. For example, Roblox says the numbers in a catalog URL are the Asset ID.

For Hoplex

If Hoplex is a game or menu that lets you enter a custom skin ID, that specific feature is not shown in the official Roblox help pages I found. The safe assumption is that Hoplex is either using avatar clothing IDs, accessory IDs, or a built-in customizer layered on top of Roblox’s normal avatar system.

Safe use

Stick to IDs from official Roblox item links or the game’s own documented UI. Avoid third-party “skin ID” lists that ask you to install extensions or share your account, since those are often unreliable and can be risky.

If you want, I can turn this into a short step-by-step guide specifically for mobile or PC.