Someone wanted the purple keyboard in this purism news

Here you go, just copy/paste the following in the file ~/.config/gtk-3.0/gtk.css
sq_button {
background-color: #362585; /* Background of the key */
color: #ffffff; /* color of the characters in the key */
}
sq_view {
background-color: #000000;
}
sq_button.altline,
sq_button.wide,
sq_button.special {
background: #151233;
}
sq_button:active,
sq_button.altline:active,
sq_button.special:active,
sq_button.wide:active {
/* Settings of the keys when you press a key */
background: #747077;
border-color: #96949d;
}
sq_button.locked {
/* Settings of the keys like 'ctrl' or 'alt' when locked */
background: #ffffff;
color: #2b292f;
}
#Return {
background: #bb1a2a;
border-color: #ff0000;
}
#Return:active {
background: #1c71d8;
border-color: #3584e4;
}