I managed to get it working like this: **$form['color_select'] = [ '#type' => 'radios', '#title' => $this->t('Pick a color'), '#options' => [ 'blue' => $this->t('Blue'), 'white' => $this->t('White'), 'black' => $this->t('Black'), // 'other' => $this->t('Other'), ], '#attributes' => [ 'id' => 'color_select', 'name' => 'color_select', ], '#states' => [ 'checked' => [ ':input[name="color_select"]' => [ ['value' => 'blue'], 'or', ['value' => 'white'], 'or', ['value' => 'black'], ], ], ], ];** Although I'm not sure how it works now. Does it actually sets the radio button on checked when the value is one of the given value ones?