Assuming that the data begin in row 2: select the range from P2 to the last used row in column P.
P2 should be the active cell in the selection,
On the Home tab of the ribbon, click Conditional Formatting > New Rule...
Select 'Format only cells that contain'.
Leave the first drop down set to 'Cell Value'.
Select 'less than' from the second drop down.
Enter the following formula in the box next to it:
=I2*25%
Note that the cell reference I2 does not contain $ signs.
Click Format...
Activate the Fill tab.
Select red.
Click OK, then click OK again.
This will color cells red if their value is less than 25% of that in column I.
Create other rules as needed.
You may have to change the order of the rules in Conditional Formatting > Manage Rules... to get the effect you want.