HI!

You need to edit: wp-content/themes/thegem/css/thegem-preloader.css 

Or use next css for changing the colors:

body #page-preloader {
    background: #2c2e3d;
}
body #page-preloader .page-preloader-spin,
body .block-preloader .page-preloader-spin,
body .preloader-spin {
    border: 2px solid transparent;
    border-top-color: #b9b7ff;
}
body .preloader-spin {
    border-top-color: #b9b7ff;
}
body #page-preloader .page-preloader-spin:before,
body .block-preloader .page-preloader-spin:before,
body .preloader-spin:before {
    border: 2px solid transparent;
    border-top-color: #00bcd4;
}
body .preloader-spin:before {
    border-top-color: #00bcd4;
}
body #page-preloader .page-preloader-spin:after,
body .block-preloader .page-preloader-spin:after,
body .preloader-spin:after {
    border: 2px solid transparent;
    border-top-color: #a3e7f0;
}
body .preloader-spin:after {
    border-top-color: #7b97ab;
}

Yes, pls. provide the wp-admin access and give me link to your gif image.

Yes, can you provide the FTP access? I'll make the code for you.

Hi,

There are no wp install on your FTP and pls. install the child theme and add link to your new preloader image.