Bring back Color display for Custom Classes #3432

I've considered several ways in which the color could be brought back. Any feedback on these options would be welcome:

• A colored circle aligned to the right, similar to how it was displayed previously.
• Rendering the name as a badge, similar to how the object labels are rendered on the map.
• Coloring the icon based on the class color.

A coloured circle or rectangle aligned to the right would be best, I think, as it not only differentiates the colours, but also gives the user an idea of what the actual Objects look like. The shape should be large enough to have both the outline and the lower-opacity fill area. I think it would be fine if all the entries in the list were made slightly taller to accommodate the possible presence of these shapes. A rectangle would probably be the best for fitting both the outline and the interior.

Rendering the name as a badge can lead to legibility issues just like the Object names currently have with certain colours, and I think it would look garish.

Colouring the icon would be very compact, but wouldn't be exactly the right colour since the icon is a complex grayscale shape, and the icon would be hard to see with certain combinations of class and theme colours. It would also miss out on the benefit of showing what the objects look like on the map.

Edit: Perhaps the icons could also be coloured, allowing value-only colours to also mean something. And classes would have the coloured rectangle to further differentiate them.

With the fill colour potentially becoming optional (#3312), these colour previews could be even more useful, since they could reflect whether the fill will be displayed.

It'd be nice if we could define colors for each custom property as well and have the tile have an rect outline (on the map and in the tile viewer and tile preview) of the colors from all the properties it has. It's very hard to visually know what tiles have custom properties and what don't. Makes it very hard to use tiled.

@jonatino Consider opening a new issue with what you'd like to see because this issue is unrelated to coloring each property or tile rect outlines. This issue is about visualizing class colors in the list of classes.