Is it it possible to extend the select trait?

I'm looking to create a trait called colours. This trait has a dropdown of colours that can be selected. When a colour is selected, I'd like to modified the class of the element to include the selected colour and remove other colours. The modifying of the class should be simple enough but I'm looking to extend the default select trait's behaviour instead of having to duplicate it for traits based around a select input.

I've tried a few things.

Extending the select type when adding the new type to the trait manager.

const selectTrait = editor.TraitManager.getType('select');
trm.addType('colours', selectTrait.extend({
    options: [
        {value: '', name: 'default'},
        {value: 'black', name: 'Black'},
        {value: 'blue', name: 'Blue'},
        // etc ...
    ],
    onValueChange: function () {
        console.log('onValueChange', this.model.get('value'));
    }
}));

And, I've attempted to change the onValueChange function (I know it's private 😉 ) when creating the component.

traits: [
    {
        type: 'select',
        label: 'colours',
        options: [
            {value: '', name: 'default'},
            {value: 'black', name: 'Black'},
            {value: 'blue', name: 'Blue'},
           // etc ...
        ],
        /**
         * On change callback
         * @private
         */
        onValueChange(model, value, opts = {}) {
            const mod = this.model;
            const trg = this.target;
            const name = mod.get('name');
            console.log(mod);
            console.log(trg);
            console.log(name);

            if (opts.fromTarget) {
                this.setInputValue(mod.get('value'));
            } else {
                const value = this.getValueForTarget();
                mod.setTargetValue(value);
            }
        },
    }

Neither seem to call my onValueChange function. Any help would be greatly appreciated. Thanks