feat: add color to preset

[tomasciccola]

should fix #182

Validation is done at the JSONSchema level by using a regex pattern in the schema itself (that only allows colors in format #rrggbb) and before encoding by using the validate-color lib.

Looking at the default config, I see there are some presets that have no color. How should we handle that? A possibility is to add a default color on the config-builder (I don't think that should live here but maybe it should??)

[EvanHahn]

wondering: should we validate when encoding that a color value is a 24-bit color string? for now, validation is done on JSONSchema level by adding a pattern with a regex in the schema itself. This means that passing an invalid string would throw. I wonder how we should handle that?
just let it throw?
Should we have a default color as a fallback? Should this default color be handled here? It could also live on the settings-builder (basically if no color or invalid color lives on a preset, then add the default one...)

IMO, we should let it throw here because the color is invalid. The settings builder seems like a great place to use a fallback.