hgk: add black and blue as preferred colors

contrib/hgk

@@ -3844,7 +3844,7 b' set maxwidth 16'
 
 set colors {green red blue magenta darkgrey brown orange}
 set authorcolors {
-    deeppink mediumorchid blue burlywood4 goldenrod slateblue red2 navy dimgrey
+    black blue deeppink mediumorchid blue burlywood4 goldenrod slateblue red2 navy dimgrey
 }
 
 catch {source ~/.hgk}