Its (hard) coded in youradmin\themes\default\template\helpers\list\list_content.tpl
{if isset($params.color) && isset($tr[$params.color])} <span class="label color_field" style="background-color:{$tr[$params.color]};color:{if !Tools::isBright($tr[$params.color])}white{else}#383838{/if}"> {/if}
And in other places for e.g. order page as this is already in twig. Check class ColorBrightnessCalculator