[NixOS] Use own picom config

nixos/home-manager.nix

@@ -1,7 +1,8 @@
-{ pkgs, ... }: {
+{ pkgs, config, ... }: {
   xsession = {
     enable = true;
     preferStatusNotifierItems = true;
+    importedVariables = [ "GDK_PIXBUF_ICON_LOADER" ];
     profileExtra = ''
       export ROFI_SYSTEMD_TERM="alacritty -e"
       . "$HOME/.lib/login.sh"
@@ -27,10 +28,6 @@
     enableSshSupport = true;
   };
 
-  services.picom = {
-    enable = true;
-  };
-
   services.blueman-applet = {
     enable = false;
   };
@@ -91,4 +88,22 @@
       }
     ];
   };
+
+  systemd.user.services.picom = {
+    Unit = {
+      Description = "Picom X11 compositor";
+      After = [ "graphical-session-pre.target" ];
+      PartOf = [ "graphical-session.target" ];
+    };
+
+    Install = { WantedBy = [ "graphical-session.target" ]; };
+
+    Service = {
+      # Temporarily fixes corrupt colours with Mesa 18.
+      Environment = [ "allow_rgb10_configs=false" ];
+      ExecStart = "${pkgs.picom}/bin/picom";
+      Restart = "always";
+      RestartSec = 3;
+    };
+  };
 }