Mark original numbers with grey background.

SudokuSolver.css

@@ -18,6 +18,10 @@ table.sudoku td.tborder {
     border-top: 2px solid black;
 }
 
+table.sudoku td.original {
+    background-color: #ccc;
+}
+
 table.sudoku td.changed {
     background-color: #fdd;
     border: 2px solid red;

coffee/SudokuBoard.class.coffee

@@ -27,6 +27,7 @@ class @SudokuBoard
             r = Math.floor(i / @dim2)
             c = i % @dim2
             @board[r][c].setValue(boardString.charAt(i))
+            @board[r][c].setOriginal(true) unless boardString.charAt(i) is '.'
             @board[r][c].resetChangeFlag()
         @setCheckDiags(alsoCheckDiags)
         console.log('Board loaded.')
@@ -57,6 +58,7 @@ class @SudokuBoard
                 cssclasses.push('tborder') if r % @dim is 0
                 cssclasses.push('lborder') if c % @dim is 0
                 cssclasses.push('changed') if @cellAt(r, c).hasChanged()
+                cssclasses.push('original') if @cellAt(r, c).isOriginal()
                 value = @cellAt(r, c).getValue()
                 if value is '.'
                     value = ''

coffee/SudokuCell.class.coffee

@@ -2,6 +2,7 @@ class @SudokuCell
     constructor: (initVal, boardObj) ->
         @boardObj = boardObj
         @changed = false
+        @original = false
         @value = 0
         @set = (1 << @boardObj.dim2) - 1   # all
         @setValue(initVal)   # init cell
@@ -46,3 +47,10 @@ class @SudokuCell
 
     resetChangeFlag: ->
         @changed = false
+
+    setOriginal: (newValue) ->
+        @original = newValue
+
+    isOriginal: ->
+        return @original
+

js/SudokuBoard.class.js

@@ -37,6 +37,9 @@
         r = Math.floor(i / this.dim2);
         c = i % this.dim2;
         this.board[r][c].setValue(boardString.charAt(i));
+        if (boardString.charAt(i) !== '.') {
+          this.board[r][c].setOriginal(true);
+        }
         this.board[r][c].resetChangeFlag();
       }
       this.setCheckDiags(alsoCheckDiags);
@@ -83,6 +86,9 @@
           if (this.cellAt(r, c).hasChanged()) {
             cssclasses.push('changed');
           }
+          if (this.cellAt(r, c).isOriginal()) {
+            cssclasses.push('original');
+          }
           value = this.cellAt(r, c).getValue();
           if (value === '.') {
             value = '';

js/SudokuCell.class.js

@@ -4,6 +4,7 @@
     function SudokuCell(initVal, boardObj) {
       this.boardObj = boardObj;
       this.changed = false;
+      this.original = false;
       this.value = 0;
       this.set = (1 << this.boardObj.dim2) - 1;
       this.setValue(initVal);
@@ -68,6 +69,14 @@
       return this.changed = false;
     };
 
+    SudokuCell.prototype.setOriginal = function(newValue) {
+      return this.original = newValue;
+    };
+
+    SudokuCell.prototype.isOriginal = function() {
+      return this.original;
+    };
+
     return SudokuCell;
 
   })();

js/SudokuSolver.class.js

@@ -295,8 +295,8 @@
         'twoValPlacesColumn': 'Only two possible places for pair in column.',
         'twoValPlacesDiag': 'Only two possible places for pair in diagonale.',
         'oneUnknownAll': 'Only one possible value left.',
-        'oneColumnForValue': 'Only one possible column for value.',
+        'oneColumnForValue': 'Only one possible column in block for value.',
-        'oneRowForValue': 'Only one possible row for value.'
+        'oneRowForValue': 'Only one possible row in block for value.'
       };
       i = 1;
       while (true) {