As Pinguin Dirk comments there is an example of exactly this in the documentation:

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

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 and MapAt:

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

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

You could also use Style but that won't fill the cell (can be finetuned by using Pane though):

{Grid[{{1, 2}, {3, Style[4, Background -> Pink]}}, Frame -> All],
 Grid[{{1, 2}, {3, Item[4, Background -> Pink]}}, Frame -> All]}

As Pinguin Dirk comments there is an example of exactly this in the documentation:

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

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 and MapAt:

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

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

You could also use Style but that won't fill the cell (can be finetuned by using Pane though):

{Grid[{{1, 2}, {3, Style[4, Background -> Pink]}}, Frame -> All],
 Grid[{{1, 2}, {3, Item[4, Background -> Pink]}}, Frame -> All]}

As Pinguin Dirk comments there is an example of exactly this in the documentation:

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

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 and MapAt:

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

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

As Pinguin Dirk comments there is an example of exactly this in the documentation:

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

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 and MapAt:

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

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

You could also use Style but that won't fill the cell (can be finetuned by using Pane though):

{Grid[{{1, 2}, {3, Style[4, Background -> Pink]}}, Frame -> All],
 Grid[{{1, 2}, {3, Item[4, Background -> Pink]}}, Frame -> All]}