diff --git a/resources/shaders/gouraud.fs b/resources/shaders/gouraud.fs
index 850d69b08..ed03bfe64 100644
--- a/resources/shaders/gouraud.fs
+++ b/resources/shaders/gouraud.fs
@@ -4,7 +4,9 @@ const vec3 ZERO = vec3(0.0, 0.0, 0.0);
 const vec3 GREEN = vec3(0.0, 0.7, 0.0);
 const vec3 YELLOW = vec3(0.5, 0.7, 0.0);
 const vec3 RED = vec3(0.7, 0.0, 0.0);
+const vec3 WHITE = vec3(1.0, 1.0, 1.0);
 const float EPSILON = 0.0001;
+const float BANDS_WIDTH = 10.0;
 
 struct SlopeDetection
 {
@@ -15,6 +17,7 @@ struct SlopeDetection
 
 uniform vec4 uniform_color;
 uniform SlopeDetection slope;
+uniform bool sinking;
 
 #ifdef ENABLE_ENVIRONMENT_MAP
     uniform sampler2D environment_tex;
@@ -23,27 +26,38 @@ uniform SlopeDetection slope;
 
 varying vec3 clipping_planes_dots;
 
-// x = tainted, y = specular;
+// x = diffuse, y = specular;
 varying vec2 intensity;
 
 varying vec3 delta_box_min;
 varying vec3 delta_box_max;
 
+varying vec4 model_pos;
+varying float world_pos_z;
 varying float world_normal_z;
 varying vec3 eye_normal;
 
+vec3 sinking_color(vec3 color)
+{
+    return (mod(model_pos.x + model_pos.y + model_pos.z, BANDS_WIDTH) < (0.5 * BANDS_WIDTH)) ? mix(color, ZERO, 0.6666) : color;
+}
+
 void main()
 {
     if (any(lessThan(clipping_planes_dots, ZERO)))
         discard;
     vec3 color = uniform_color.rgb;
     float alpha = uniform_color.a;
-    if (slope.actived && world_normal_z < slope.normal_z - EPSILON) {
+    if (slope.actived && world_normal_z < slope.normal_z - EPSILON)
+    {
         color = vec3(0.7, 0.7, 1.0);
         alpha = 1.0;
     }
     // if the fragment is outside the print volume -> use darker color
 	color = (any(lessThan(delta_box_min, ZERO)) || any(greaterThan(delta_box_max, ZERO))) ? mix(color, ZERO, 0.3333) : color;
+    // if the object is sinking, shade it with inclined bands or white around world z = 0
+    if (sinking)
+        color = (abs(world_pos_z) < 0.05) ? WHITE : sinking_color(color);
 #ifdef ENABLE_ENVIRONMENT_MAP
     if (use_environment_tex)
         gl_FragColor = vec4(0.45 * texture2D(environment_tex, normalize(eye_normal).xy * 0.5 + 0.5).xyz + 0.8 * color * intensity.x, alpha);
diff --git a/resources/shaders/gouraud.vs b/resources/shaders/gouraud.vs
index ed7e3f56b..f2706b386 100644
--- a/resources/shaders/gouraud.vs
+++ b/resources/shaders/gouraud.vs
@@ -41,7 +41,7 @@ uniform vec2 z_range;
 // Clipping plane - general orientation. Used by the SLA gizmo.
 uniform vec4 clipping_plane;
 
-// x = tainted, y = specular;
+// x = diffuse, y = specular;
 varying vec2 intensity;
 
 varying vec3 delta_box_min;
@@ -49,6 +49,8 @@ varying vec3 delta_box_max;
 
 varying vec3 clipping_planes_dots;
 
+varying vec4 model_pos;
+varying float world_pos_z;
 varying float world_normal_z;
 varying vec3 eye_normal;
 
@@ -69,12 +71,16 @@ void main()
     NdotL = max(dot(eye_normal, LIGHT_FRONT_DIR), 0.0);
     intensity.x += NdotL * LIGHT_FRONT_DIFFUSE;
 
+    model_pos = gl_Vertex;
+    // Point in homogenous coordinates.
+    vec4 world_pos = print_box.volume_world_matrix * gl_Vertex;
+    world_pos_z = world_pos.z;
+
     // compute deltas for out of print volume detection (world coordinates)
     if (print_box.actived)
     {
-        vec3 v = (print_box.volume_world_matrix * gl_Vertex).xyz;
-        delta_box_min = v - print_box.min;
-        delta_box_max = v - print_box.max;
+        delta_box_min = world_pos.xyz - print_box.min;
+        delta_box_max = world_pos.xyz - print_box.max;
     }
     else
     {
@@ -86,8 +92,6 @@ void main()
 	world_normal_z = slope.actived ? (normalize(slope.volume_world_normal_matrix * gl_Normal)).z : 0.0;
 
     gl_Position = ftransform();
-    // Point in homogenous coordinates.
-    vec4 world_pos = print_box.volume_world_matrix * gl_Vertex;
     // Fill in the scalars for fragment shader clipping. Fragments with any of these components lower than zero are discarded.
     clipping_planes_dots = vec3(dot(world_pos, clipping_plane), world_pos.z - z_range.x, z_range.y - world_pos.z);
 }
diff --git a/src/slic3r/GUI/3DScene.cpp b/src/slic3r/GUI/3DScene.cpp
index ba62576f2..57ec1e0d9 100644
--- a/src/slic3r/GUI/3DScene.cpp
+++ b/src/slic3r/GUI/3DScene.cpp
@@ -345,9 +345,16 @@ void GLVolume::set_render_color(const float* rgba, unsigned int size)
 
 void GLVolume::set_render_color()
 {
-    if (force_native_color || force_neutral_color)
-    {
+#if ENABLE_ALLOW_NEGATIVE_Z
+    bool outside = is_outside || is_below_printbed();
+#endif // ENABLE_ALLOW_NEGATIVE_Z
+
+    if (force_native_color || force_neutral_color) {
+#if ENABLE_ALLOW_NEGATIVE_Z
+        if (outside && shader_outside_printer_detection_enabled)
+#else
         if (is_outside && shader_outside_printer_detection_enabled)
+#endif // ENABLE_ALLOW_NEGATIVE_Z
             set_render_color(OUTSIDE_COLOR, 4);
         else {
             if (force_native_color)
@@ -362,17 +369,24 @@ void GLVolume::set_render_color()
         else if (hover == HS_Deselect)
             set_render_color(HOVER_DESELECT_COLOR, 4);
         else if (selected)
+#if ENABLE_ALLOW_NEGATIVE_Z
+            set_render_color(outside ? SELECTED_OUTSIDE_COLOR : SELECTED_COLOR, 4);
+#else
             set_render_color(is_outside ? SELECTED_OUTSIDE_COLOR : SELECTED_COLOR, 4);
+#endif // ENABLE_ALLOW_NEGATIVE_Z
         else if (disabled)
             set_render_color(DISABLED_COLOR, 4);
+#if ENABLE_ALLOW_NEGATIVE_Z
+        else if (outside && shader_outside_printer_detection_enabled)
+#else
         else if (is_outside && shader_outside_printer_detection_enabled)
+#endif // ENABLE_ALLOW_NEGATIVE_Z
             set_render_color(OUTSIDE_COLOR, 4);
         else
             set_render_color(color, 4);
     }
 
-    if (!printable)
-    {
+    if (!printable) {
         render_color[0] /= 4;
         render_color[1] /= 4;
         render_color[2] /= 4;
@@ -504,6 +518,21 @@ void GLVolume::render() const
 bool GLVolume::is_sla_support() const { return this->composite_id.volume_id == -int(slaposSupportTree); }
 bool GLVolume::is_sla_pad() const { return this->composite_id.volume_id == -int(slaposPad); }
 
+#if ENABLE_ALLOW_NEGATIVE_Z
+bool GLVolume::is_sinking() const
+{
+    if (is_modifier)
+        return false;
+    const BoundingBoxf3& box = transformed_convex_hull_bounding_box();
+    return box.min(2) < 0.0 && box.max(2) >= 0.0;
+}
+
+bool GLVolume::is_below_printbed() const
+{
+    return transformed_convex_hull_bounding_box().max(2) < 0.0;
+}
+#endif // ENABLE_ALLOW_NEGATIVE_Z
+
 std::vector<int> GLVolumeCollection::load_object(
     const ModelObject       *model_object,
     int                      obj_idx,
@@ -778,6 +807,9 @@ void GLVolumeCollection::render(GLVolumeCollection::ERenderType type, bool disab
         shader->set_uniform("print_box.volume_world_matrix", volume.first->world_matrix());
         shader->set_uniform("slope.actived", m_slope.active && !volume.first->is_modifier && !volume.first->is_wipe_tower);
         shader->set_uniform("slope.volume_world_normal_matrix", static_cast<Matrix3f>(volume.first->world_matrix().matrix().block(0, 0, 3, 3).inverse().transpose().cast<float>()));
+#if ENABLE_ALLOW_NEGATIVE_Z
+        shader->set_uniform("sinking", volume.first->is_sinking());
+#endif // ENABLE_ALLOW_NEGATIVE_Z
 
         volume.first->render();
     }
diff --git a/src/slic3r/GUI/3DScene.hpp b/src/slic3r/GUI/3DScene.hpp
index 25c5443cd..2d46a4524 100644
--- a/src/slic3r/GUI/3DScene.hpp
+++ b/src/slic3r/GUI/3DScene.hpp
@@ -453,6 +453,11 @@ public:
     bool                is_sla_support() const;
     bool                is_sla_pad() const;
 
+#if ENABLE_ALLOW_NEGATIVE_Z
+    bool                is_sinking() const;
+    bool                is_below_printbed() const;
+#endif // ENABLE_ALLOW_NEGATIVE_Z
+
     // Return an estimate of the memory consumed by this class.
     size_t 				cpu_memory_used() const { 
     	//FIXME what to do wih m_convex_hull?