Hi there,
Please add this following css on child theme style.css file to change color of post comment.
.single-post .btn.green {
background-color: #f597cc;
}
Note: You can change background color value as per your requirement. You can see here for different color code:
http://www.w3schools.com/cssref/css_colors.asp
And to change background color on hover you use this css:
.btn.green:hover, .btn.green:focus, .btn.green:active, .btn.green.active {
background-color: #f597cc;
color: #fff;
}
Here also you can change the background color value as per your requirement. You can see here for different color code:
http://www.w3schools.com/cssref/css_colors.asp
Note: Please use child theme style.css file to add custom css otherwise your changes will lost on theme update
Let us know how it will goes.
Thanks