Modify label_attr field in Symfony 6 form builder

I can change the class of my inputs, but not for my labels. How can I change class of my dynamics labels . I can't when I use 'label_attr', because it's a type Closure.

$builder
        ->add('skill', EntityType::class, [
            'class' => Skill::class,
            'query_builder' => function (SkillRepository $r) {
                return $r->createQueryBuilder('i')
                    ->orderBy('i.color', 'ASC');
            },
            'label' => 'Mes compétences',
            // input OK !
            'choice_attr' => function (?Skill $color) {
                return $color ? ['class' => 'color_'.$color->getColor()] : [];
            },
            // ERROR
            'label_attr' => function (?Skill $color) {
                return $color ? ['class' => 'color_'.$color->getColor()] : [];
            },

            'attr' => [
                'class' => 'btn'
            ],
            'choice_label' => 'name',
            
            'multiple' => true,
            'expanded' => true,
        ])

An error has occurred resolving the options of the form "Symfony\Bridge\Doctrine\Form\Type\EntityType": The option "label_attr" with value Closure is expected to be of type "array", but is of type "Closure".

            // ERROR
            'label_attr' => function (?Skill $color) {
                return $color ? ['class' => 'color_'.$color->getColor()] : [];
            },