diff --git a/doc/src/sgml/images/README b/doc/src/sgml/images/README
index 07c4580255..c451d4bca4 100644
--- a/doc/src/sgml/images/README
+++ b/doc/src/sgml/images/README
@@ -13,7 +13,8 @@ involve diffable source files.
 These tools are acceptable:
 
 - Graphviz (https://graphviz.org/)
-- Ditaa (http://ditaa.sourceforge.net/)
+- Ditaa (https://github.com/stathissideris/ditaa), version 0.11 or
+  higher. Previous versions does not support SVG.
 
 We use SVG as the format for integrating the image into the ultimate
 output formats of the documentation, that is, HTML, PDF, and others.
diff --git a/doc/src/sgml/images/gin.gv b/doc/src/sgml/images/gin.gv
index 097e91029a..35520736ec 100644
--- a/doc/src/sgml/images/gin.gv
+++ b/doc/src/sgml/images/gin.gv
@@ -1,85 +1,101 @@
 digraph "gin" {
+
         layout=dot;
-        node [label="", shape=box, style=filled, fillcolor=gray, width=1.4];
 
-        m1 [label="meta page"];
+        // default values
+        node  [shape=box, label="", fontname="sans-serif", style=filled, fillcolor=lightgray, width=1.4];
+        graph [fontname="sans-serif"]; // must be specified separately
+        edge  [fontname="sans-serif"]; // must be specified separately
+
+        // an unobtrusive background color
+        pad="1.0, 0.5";
+        bgcolor=whitesmoke;
 
+        // The top node
+        m1 [label="meta page", style=filled, fillcolor=beige];
+
+        // other nodes
         subgraph cluster01 {
-                label="entry tree";
-                subgraph egroup1 {
-                        rank=same;
-                        e1;
-                }
-                subgraph egroup2 {
-                        rank=same;
-                        e2 -> e3 -> e4;
-                }
-                subgraph egroup3 {
-                        rank=same;
-                        e5 -> e6 -> e7 -> e8 -> e9;
-                }
-                e1 -> e4;
-                e1 -> e3;
-                e1 -> e2;
-                e2 -> e5;
-                e2 -> e6;
-                e3 -> e7;
-                e4 -> e8;
-                e4 -> e9;
-
-                e6 [fillcolor=green, label="posting list"];
-                e8 [fillcolor=green, label="posting list"];
-                e9 [fillcolor=green, label="posting list"];
+                 bgcolor=white;
+                 label="entry tree";
+                 subgraph egroup1 {
+                          rank=same;
+                          e1;
+                  }
+                  subgraph egroup2 {
+                           rank=same;
+                           e2 -> e3 -> e4;
+                  }
+                  subgraph egroup3 {
+                           rank=same;
+                           e5 -> e6 -> e7 -> e8 -> e9;
+                  }
+                  e1 -> e4;
+                  e1 -> e3;
+                  e1 -> e2;
+                  e2 -> e5;
+                  e2 -> e6;
+                  e3 -> e7;
+                  e4 -> e8;
+                  e4 -> e9;
+
+                  e5 [fillcolor=cyan];
+                  e6 [fillcolor=cyan];
+                  e7 [fillcolor=cyan];
+                  e8 [fillcolor=cyan];
+                  e9 [fillcolor=cyan];
+
         }
 
         subgraph cluster02 {
-                label="posting tree";
-                subgraph pgroup1 {
-                        rank=same;
-                        p1;
-                }
-                subgraph pgroup2 {
-                        rank=same;
-                        p2 -> p3;
-                }
-                p1 -> p2;
-                p1 -> p3;
-
-                p2 [fillcolor=green, label="heap ptr"];
-                p3 [fillcolor=green, label="heap ptr"];
+                 bgcolor=white;
+                 label="posting tree";
+                 subgraph pgroup1 {
+                          p1;
+                 }
+                 subgraph pgroup2 {
+                          rank=same;
+                          p2 -> p3;
+                 }
+                 p1 -> p2;
+                 p1 -> p3;
+
+                 p2 [fillcolor=deepskyblue];
+                 p3 [fillcolor=deepskyblue];
         }
 
         subgraph cluster03 {
-                label="posting tree";
-                subgraph pgroup3 {
-                        rank=same;
-                        p4;
-                }
+                 bgcolor=white;
+                 label="posting tree";
+                 subgraph pgroup3 {
+                          p4;
+                 }
 
-                p4 [fillcolor=green, label="heap ptr"];
+                 p4 [fillcolor=deepskyblue];
         }
 
         subgraph cluster04 {
-                label="posting tree";
-                subgraph pgroup4 {
-                        rank=same;
-                        p5;
-                }
-                subgraph pgroup5 {
-                        rank=same;
-                        p6 -> p7;
-                }
-                p5 -> p6;
-                p5 -> p7;
-
-                p6 [fillcolor=green, label="heap ptr"];
-                p7 [fillcolor=green, label="heap ptr"];
+                 bgcolor=white;
+                 label="posting tree";
+                 subgraph pgroup4 {
+                          p5;
+                 }
+                 subgraph pgroup5 {
+                          rank=same;
+                          p6 -> p7;
+                 }
+                 p5 -> p6;
+                 p5 -> p7;
+
+                 p6 [fillcolor=deepskyblue];
+                 p7 [fillcolor=deepskyblue];
         }
 
         subgraph cluster05 {
-                label="pending list";
-                node [style=filled, fillcolor=red];
-                n1 -> n2 -> n3 -> n4;
+                 bgcolor=white;
+                 label="pending list";
+                 node [fillcolor=wheat, label="pending entries", width=1.8];
+                 n1 -> n2 -> n3 -> n4 -> n5;
         }
 
         m1 -> e1;
@@ -88,6 +104,12 @@ digraph "gin" {
         e7 -> p5;
         m1 -> n1;
 
-        e5 [style=filled, fillcolor=green4];
-        e7 [style=filled, fillcolor=green4];
+        // Explanations
+        expl_1 [shape=plaintext,                 width=2.5, label="Internal tree node"];
+        expl_2 [shape=plaintext, fillcolor=cyan, width=5.2, label="<posting list> and/or pointer to <posting tree>"];
+        expl_3 [shape=plaintext, fillcolor=deepskyblue, width=2.0, label="Only <posting list>"];
+        p6 -> expl_1 [style=invis];
+        p6 -> expl_2 [style=invis];
+        p6 -> expl_3 [style=invis];
+
 }