Iterate through Super Table field in plugin
Assuming your Super Table field has a handle of colors, you should be able to do:

foreach ($entry-&gt;colors as $block) {
    // Color will return a category element query, so you can do:

    // Return a collection of all category ids
    Craft::dump($block-&gt;color-&gt;ids());

    // Get the first category
    Craft::dump($block-&gt;color-&gt;one());

    // Get all the categories in the field
    Craft::dump($block-&gt;color-&gt;all());
}