Add a "Background Class" select field to Beaver Builder row "Advanced" tab.

bb-row-advanced-bg-class-field.php

<?php

/**
 * Add a "Background Class" setting to the row, advanced, CSS selectors section.
 */
add_filter('fl_builder_register_settings_form', function (array $form, string $id): array {
    if ('row' !== $id) {
        return $form;
    }

    $form['tabs']['advanced']['sections']['css_selectors']['fields']['background_class'] = [
        'type' => 'select',
        'label' => __('Background Class', 'avado'),
        'default' => 'bg-color-default',
        'options' => get_background_colours(),
    ];

    return $form;
}, 10, 2);

/**
 * Adds the chosen "Background class" to the row.
 */
add_filter('fl_builder_row_attributes', function (array $attrs, object $row): array {
    if ('row' !== $row->type) {
        return $attrs;
    }

    if ('bg-color-default' === $row->settings->background_class) {
        return $attrs;
    }

    $attrs['class'][] = $row->settings->background_class;

    return $attrs;
}, 10, 2);