>I noticed that when I type NULL in my code VFP automatically sets the font color of the word in blue. Whereas if I type it as .NULL. (with period before and after), it stays unchanged. It seems like VFP treats NULL as a special word vs. .NULL. Is there really a difference? Or what is the better practice?

There's no difference but I prefer NULL because it's the same in MS SQL Server.
The same goes for OR AND NOT