You’re interested in changing the color of all the table borders or just the outside borders? Below are steps for changing the color of all the table borders.
Add a custom class to your table shortcode (let’s say class="custom-border", so the first part of the table shortcode will be like this: [su_table class="custom-border"]), and then add the following to the Additional CSS section of your site (in Appearance > Customize via your WordPress admin panel), changing the hex color code (#8D33FF) to your desired color:
div.su-table.custom-border.su-table-alternate > table > tbody > tr > td { border: 1px solid #8D33FF !important; }
