Please follow the instruction below to change the arrow colour:
Install and active child theme.
1) Don’t forget to take a backup of the file prior to any change.
2) Login to the admin dashboard. Navigate appearance -> Editor menu.
3) On the stylesheet (style.css) file, please add the following style.
section.fullwidth.site-slider .slide-down i {
color: #FD0; // You can change this colour to your colour
}
4) Update the file.