JAL-3111 tweak PCA documentation

diff --git a/help/html/calculations/pca.html b/help/html/calculations/pca.html
index 5b76d10..3529cae 100755 (executable)
--- a/help/html/calculations/pca.html
+++ b/help/html/calculations/pca.html
@@ -78,8 +78,10 @@
     within the similarity space, as points in a rotateable 3D
     scatterplot. The colour of each sequence point is the same as the
     sequence group colours, white if no colour has been defined for the
     within the similarity space, as points in a rotateable 3D
     scatterplot. The colour of each sequence point is the same as the
     sequence group colours, white if no colour has been defined for the

-    sequence, and green if the sequence is part of a the currently
-    selected group.</p>
+    sequence, and grey if the sequence is part of the currently selected
+    group. The viewer also employs depth cueing, so points appear darker
+    the farther away they are, and become brighter as they are rotated
+    towards the front of the view.</p>

   <p>
     The 3d view can be rotated by dragging the mouse with the <strong>left
       mouse button</strong> pressed. The view can also be zoomed in and out with
   <p>
     The 3d view can be rotated by dragging the mouse with the <strong>left
       mouse button</strong> pressed. The view can also be zoomed in and out with