Why this would be helpful

The current color picker in Scratch only provides three sliders (Color, Saturation, Brightness), which makes it less intuitive for creators to pick colors quickly and accurately. Professional design and art tools (like Photoshop, SAI, or vector design software) all use a square HSV/HSB color palette.

Adding an HSV square palette addon would drastically improve the user experience for artists and animators in Scratch. It allows users to visually understand the relationship between saturation and brightness at a glance, making color selection much faster, more precise, and aligned with standard digital art workflows.

How this addon works

1. Add a toggle button at the bottom center of the scratch color picker menu (between or next to existing buttons).
2. Clicking this button toggles the view of the color picker:
   • It hides the default three sliders (Color, Saturation, Brightness).
   • It displays a standard HSV square color palette, with a saturation-brightness square on the left and a vertical hue color bar on the right.
3. Clicking the toggle button again switches the view back to the original three sliders.
4. The addon should seamlessly sync the selected HSV values back to the Scratch VM so that costumes and pen colors update in real-time.

Possible alternatives

The only alternative currently is for users to use an external professional software (or online color picker websites) to find the color they want, copy the hex code or RGB values, and then manually adjust the three sliders in Scratch to match it. This completely breaks the creative workflow and is highly inefficient.

Additional context

This feature is inspired by professional digital painting interfaces. To minimize implementation effort, the addon could potentially leverage lightweight, open-source color picker libraries like @jaames/iro (Iro.js) or Vanilla-Picker, and style it to fit Scratch's default UI theme.

Attached is a conceptual reference image of the HSV square layout: