style.css içerisinde alttaki renk kodlarını değiştirmeyi denediniz mi?

.ro-hr-heading:after {
content:" ";
display:block;
width:50px;
margin:30px auto 0 auto;
height:1px;
transition:all 0.4s;
background:#a360ff;
background:-moz-linear-gradient(left,#a360ff 0%,#0084ff 100%);
background:-webkit-gradient(left top,right top,color-stop(0%,#a360ff),color-stop(100%,#0084ff));
background:-webkit-linear-gradient(left,#a360ff 0%,#0084ff 100%);
background:-o-linear-gradient(left,#a360ff 0%,#0084ff 100%);
background:-ms-linear-gradient(left,#a360ff 0%,#0084ff 100%);
background:linear-gradient(to right,#a360ff 0%,#0084ff 100%);
}