As [Pinguin Dirk][1] comments there is an example of exactly this in [the documentation](http://reference.wolfram.com/mathematica/ref/Grid.html#1018545094):

    Grid[Table[x, {4}, {7}],
      Background -> {None, None, {{1, 1} -> Pink, {3, 3} -> Red}}]

![enter image description here][2]

Those who value brevity may wish to note that implicit `Null` may be used in place of `None`:

    Background -> {, , {{1, 1} -> Pink, {3, 3} -> Red}}

You can also use [`Item`](http://reference.wolfram.com/mathematica/ref/Item.html) and [`MapAt`](http://reference.wolfram.com/mathematica/ref/MapAt.html):

    tbl = Table[x, {4}, {7}];

    MapAt[Item[#, Background -> Pink] &, tbl, {{3, 3}, {2, 6}}] // Grid

![enter image description here][3]


  [1]: http://mathematica.stackexchange.com/users/5274/pinguin-dirk
  [2]: https://i.sstatic.net/oJl3w.gif
  [3]: https://i.sstatic.net/qrsi6.png