Try Conditional Formatting
Suppose you want this to happen in say, col E
Select col E
Click Format > Conditional Formatting
Make the settings as:
For Condition 1:
Formula Is| =AND(E1<>"",ISNUMBER(E1),E1>=0)
Click Format button > Patterns tab > Light green? > OK
Click Add
For Condition 2:
Formula Is| =AND(E1<>"",ISNUMBER(E1),E1<0)
Click Format button > Patterns tab > Pink? > OK
Click OK at the main dialog
Now test it out by inputting some negative, positive values, zeroes and some
text (e.g.: "ABC") in col E ..
The cells' fill color should appear accordingly for the numbers, any cell
with text entered or empty cells should not trigger the C.F. (i.e. no
formatting should occur)