gray text color does not change

It’s coming through because of this in your light.css stylesheet:

.blog-post-title .blog-post-title-wrapper ul > li > span, .blog-post-title .blog-post-title-wrapper-full ul > li > span {

Try this in your stylesheet or the the plugins Styles page.

.crp_related.crp-grid ul > li > span.crp_excerpt {
  color: black;
}

Thank you for confirming. Please do consider a review of the plugin.

https://ww.wp.xz.cn/support/plugin/contextual-related-posts/reviews/