Hi there,

.hamburger span {

    background-color: white;

}

.hamburger span::before, .hamburger span::after {

   background-color: white;

}

.hamburger-rotate.is-active span::before {

 background-color: white;

}

.hamburger-rotate.is-active span::after{

 background-color: white;

}

Replace white with any color. add the css in theme options -. styling options -> custom css

Thanks