Just wondering another code. It doesn't work on a user that has spaces:
li[data-user="FFoxyThePirateFox"] .username {
color: #B378D3;
}
li[data-user="Bonnie_the_Kawaii_Rabbit"] .username {
color: #FFA500;
}
li[data-user="Gerardluis23"] .username {
color: #ffff00;
}