Hi Bouke,
– It is actually possible to change the URL scheme for the user result on the General Options -> User search panel. I have made the change for you for the desired scheme: https://i.imgur.com/4Cxoy88.png
– Of course. You can change that background color with this custom CSS:
[html]fieldset.asp_custom_f select[multiple] {
background: red !important;
}[/html]