Please follow the instructions to fix the issue.
1. Create a new layout XML file in your theme
app/design/frontend/Vendor/theme/Magento_Swatches/layout/catalogsearch_result_index.xml
2. Put content
<?xml version="1.0"?>
<!--
/**
* Copyright © 2015 Magento. All rights reserved.
* See COPYING.txt for license details.
*/
-->
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="2columns-left"
xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<head>
<css src="Magento_Swatches::css/swatches.css"/>
</head>
<body>
<referenceBlock name="category.product.type.details.renderers">
<block class="Magento\Swatches\Block\Product\Renderer\Listing\Configurable" as="configurable"
template="Magento_Swatches::product/listing/renderer.phtml" />
</referenceBlock>
</body>
</page>3. Save the file and flush the Magento cache
4. Vuala :-)
