diff --git a/tests/rails.scad b/tests/rails.scad
index f91b950..2a72118 100644
--- a/tests/rails.scad
+++ b/tests/rails.scad
@@ -34,7 +34,7 @@ module rails()
             nut = screw_nut(screw);
             washer = screw_washer(screw);
 
-            rail_assembly(rail, length, rail_travel(rail, length) / 2);
+            rail_assembly(rail, length, rail_travel(rail, length) / 2, $i<2 ? grey20 : "green", $i<2 ? grey20 : "red");
 
             rail_screws(rail, length, sheet + nut_thickness(nut, true) + washer_thickness(washer));
 
diff --git a/vitamins/rail.scad b/vitamins/rail.scad
index c202b39..db42e4a 100644
--- a/vitamins/rail.scad
+++ b/vitamins/rail.scad
@@ -65,7 +65,7 @@ module carriage_hole_positions(type) { //! Position children over screw holes
                 children();
 }
 
-module carriage(type, rail) { //! Draw the specified carriage
+module carriage(type, rail, end_color = grey20, wiper_color = grey20) { //! Draw the specified carriage
     total_l = carriage_length(type);
     block_l = carriage_block_length(type);
     block_w = carriage_width(type);
@@ -103,14 +103,14 @@ module carriage(type, rail) { //! Draw the specified carriage
     }
 
     module carriage_end(type, end_w, end_h, end_l) {
-        red_length = 0.5;
-        color("red") translate_z(-end_l/2) linear_extrude(red_length)
+        wiper_length = 0.5;
+        color(wiper_color) translate_z(-end_l/2) linear_extrude(wiper_length)
             difference() {
                 translate([-end_w/2, carriage_clearance(type)])
                     square([end_w, end_h]);
                 cutout();
             }
-        color("green") translate_z(red_length-end_l/2) linear_extrude(end_l-red_length)
+        color(end_color) translate_z(wiper_length-end_l/2) linear_extrude(end_l-wiper_length)
             difference() {
                 translate([-end_w/2, carriage_clearance(type)])
                     square([end_w, end_h]);
@@ -150,11 +150,11 @@ module rail(type, length) { //! Draw the specified rail
     }
 }
 
-module rail_assembly(type, length, pos) { //! Rail and carriage assembly
+module rail_assembly(type, length, pos, carriage_end_color = grey20, carriage_wiper_color = grey20) { //! Rail and carriage assembly
     rail(type, length);
 
     translate([pos, 0])
-        carriage(rail_carriage(type), type);
+        carriage(rail_carriage(type), type,  carriage_end_color, carriage_wiper_color);
 
 }