Cosmetic Items are usually changing the visual representation of the Cutie in-game and is an off-chain item, that does not interact with the blockchain.
There are a couple of these items at this time:
Standard wallpaper changes a Noble Cutie's background pattern.
The pattern is the semi-transparent design on noble Cutie's background.
These wallpapers can be applied several times to a Cutie. Each additional application adds more details to the Cutie's background.
These wallpapers are usually released as a limited-time run alongside events and seasons.
Color spray changes Cutie's background color. The color ranges are different for the 3 different rarities of the Color Spray available in the game.
Rainbow Color Spray - Changes to a solid color
Rare Rainbow Color Spray - Changes to a gradient of up to 2 colors
Super Rare Rainbow Color Spray - Changes to a gradient of up to 3 colors
Some equipable items can change a Cutie's visual representation when it's hidden as an easter egg. For example - a strange trinket added to the Bone Dragon changes its eyes to glow green and breathe green fumes.