Hi,

Do  you want change color of h2-h6 tags on content post ?

If right, please go to Customize > Addtional CSS then add custom css to do that:

.wpb_text_column h2, .wpb_text_column h3,.wpb_text_column h4,.wpb_text_column h5,.wpb_text_column h6,
.entry-content h2,  .entry-content h3, .entry-content h4, .entry-content h5,.entry-content h6, 
.comment-content h2, .comment-content h3, .comment-content h4, .comment-content h5, .comment-content h6{
 color:red;
}

You can change color red to any color you want

Best Regards,

PenciDesign