scratch-userscripts/scratch-colorful-messages.css

.social-message {
  border-bottom-color: #C5C5C5;
}

.social-message.mod-forum-activity {
  background-color: hsl(300, 55%, 92%);
}

.social-message.mod-comment-message,
.social-message.mod-follow-user {
  background-color: hsl(215, 100%, 90%);
}

.social-message.mod-curator-invite,
.social-message.mod-become-manager,
.social-message.mod-studio-activity {
  background-color: hsl(163, 60%, 85%);
}

.social-message.mod-love-favorite {
  background-color: hsl(45, 90%, 95%);
}

.social-message.mod-love-project {
  background-color: hsl(350, 100%, 95%);
}

.social-message.mod-remix-project {
  background-color: hsl(260, 100%, 90%);
}

.social-message.mod-unread {
  background-color: hsl(100, 95%, 95%);
  box-shadow: 0 2px 3px -2px rgba(0, 200, 200, 80%);
  position: relative;
}