Create generic colour 'rainbow' swatch, which enables users to assign colours to mixer channels, percussion, etc.

[Tantacrul]

Here's an example of what Reason offers.

This colour swatch would not be affected by the accent colour. We would most likely need two different swatches for dark / light mode.

[jessjwilliamson]

This task has been completed and is ready to be implemented For accessibility reasons, the names of each color are also listed. All of this is in the 'UI Components & Styles' > 'Colors' page

[jessjwilliamson]

Dev task raised in https://github.com/musescore/MuseScore/issues/17714