您需要获取直接父对象的颜色，或者循环遍历所有Ansestor，直到找到颜色为止
如果未找到颜色，则获取默认值并输出。

我对结构做了一些更改，并为每个步骤添加了所有注释。

请注意，为了获得相同的结果，我提供了两个选项，请选择一个适合您需要的选项。

// get category terms of the current post
if ($terms = get_the_terms( get_the_ID(),\'category\')) {
    // prepare the output for sprintf
    // to avoid repeating ourselves we can create a variable to conatin the output
    // %s is a sting placeholder
    $output = \'<div class="post_loop-cat" style="background-color: %s;">%s</div>\';

    // unless you always have one categpry for every post
    // this will always set $cat_id to the last $term of the loop, always
    // take this into account
    foreach ($terms as $term) {
        $cat_id = $term->term_id;
    }

    // get ACF category color
    $cat_color = get_field(\'category-color\', \'category_\' . $cat_id);

    // because we don\'t know the depth of the category
    // or how high do you want to go to get the parent color
    // we can do either of the following
    // in both options we will first check if $cat color exists

    // option 1
    // using the direct parent only

    if ($cat_color) { // color found, output the html
        echo sprintf($output, $cat_color, $term->name);
    } else {
        // get the parent category color
        $cat_color = get_field(\'category-color\', \'category_\' . $term->parent);

        // if not found, set color to default
        if (empty($cat_color)) $cat_color = get_field(\'primary-color\', \'option\');

        // output the html
        echo sprintf($output, $cat_color, $term->name);
    }

    // option 2
    // using the category ancestors to find the color
    // we loop each ancestor, once we found a color we stop and output

    if ($cat_color) { // color found, output the html
        echo sprintf($output, $cat_color, $term->name);
    } else {
        // get and loop all ansestors
        foreach (get_ancestors($cat_id, \'category\') as $ancestor_id) {
            // get and check category color, if found, break out of the loop
            if ($cat_color = get_field(\'category-color\', \'category_\' . $ancestor_id)) break;
        }

        // if not found, set color to default
        if (empty($cat_color)) $cat_color = get_field(\'primary-color\', \'option\');

        // output the html
        echo sprintf($output, $cat_color, $term->name);
    }
}