Yes it is, use Format | Conditional Formatting from the menu toolbar.
Whether you use the 'Cell Value Is' or the 'Formula Is' option depends on how
things are set up on your worksheet/in the cells.
If you already have a formula in the cell to shade, then use the 'Cell Value
Is' option, and if you're just changing the shade based on the value in some
other cell, then use the 'Formula Is' option.