Line 3415 in your CSS. Notice the colors in Epik are all listed. You need to change the color in that section, or any section to make it your own choice.
Here is the simple .css change of existing green to a different color green:
.epik-green .head-wrap,
.epik-green .welcome,
.epik-green .home-feature-bg-dark,
.epik-green .author-box,
.epik-green .footer-widgets {
background: #1c3f1a;
color: #eee;
}