With this method you can quickly color the empty cells in the worksheet.

1. Select the specified range where you will shade all blank cells (or nonblank cells).

2. Click Home > Find & Select > Go To Special…to open the Go To Special dialog box. And then check the Blanks option in this dialog box, see screenshot:
Note: For selecting all nonblank cells, please check the Constants option.

3. Click OK. And all of the blank cells (or nonblank cells) have been selected in the specified range.

4. And then click Home > Fill Color and choose the color you'd like to fill. See screenshot:

And all of the empty cells (or nonblank cells) have been shaded.

You can also apply Conditional Formatting to shade blank (or nonblank) cells. With this method, when you enter data into a blank cell (or remove data from a nonblank cell), the shading color in this cell will be restored to the default color. You can do as follows:

1. Select the range where you will shade all blank (or nonblank) cells. See screenshot:

2. Then click Home > Conditional Formatting > New Rule to open the New Formatting Rule dialog box.

3. In the opening dialog box, please click Use a formula to determine which cells to format in the Select a Rule Type box, and enter the formula =A1= "" (A1 is the first cell in the specified range) into the Format values where this formula is true box, and click the Format button.
Note: For shading all nonblank cells in the specified range, please enter this formula =A1<>"" into the Format values where this formula is true box.

4. Then in the Format Cell dialog box, select a fill color on the Fill tab, and click the OK button.

5. And it will return to the New Formatting Rule dialog box, you can preview the color in the Preview box, and please click the OK button to apply this conditional formatting.
All of the blank cells (or nonblank cells) in the specified range have been shaded. When you type some data into the colored blank cells (or remove data from nonblank cells), the cell will return to the default background color.

This method will guide you apply Kutools for Excel’s Select Nonblank Cells utility to select all nonblank cells in a specified range, and then color them easily in Excel.

1. Select the range where you will color all nonblank cells together, and click Kutools > Select > Select Nonblank Cells. See screenshot:

Then a dialog box will come out and tell you how many nonblank cells have been selected. Click the OK button to close it. See screenshot above.

2. Add fill color for these selected cell by clicking Home > Fill Color and selecting a fill color from drop down list. See screenshot:

So far we have colored all nonblank cells together in the specified range as below screenshot shown: