style.css

.ct-chart .ct-series-a .ct-line {
    stroke: red;

}

.ct-chart .ct-series-b .ct-line {
    stroke: #4F2112;
}

.ct-chart .ct-series-c .ct-line {
    stroke: green;
}

.ct-chart .ct-series-d .ct-line {
    stroke: blue;
}

.ct-legend {
    padding-left: 70px;
}

/* basic positioning */
.ct-legend {
    list-style: none;
}

.ct-legend li {
    float: left;
    margin-right: 10px;
}

.ct-legend span {
    border: 1px solid #ccc;
    float: left;
    width: 12px;
    height: 12px;
    margin: 2px;
}

/* your colors */
.ct-legend .ct-series-0 span {
    background-color: red;
    font-size: 1.5em;
}

.ct-legend .ct-series-1 span {
    background-color: #4F2112;;
}

.ct-legend .ct-series-2 span {
    background-color: green;
}

.ct-legend .ct-series-3 span {
    background-color: blue;
}