There are two excel workbooks are connected by (=[Book1.xlsx]Sheet1!$A$1) but there are two user A and B, I just want when a enter something in cell it show in red font color & when B enter something in cell it shows in Blue font color. Please some one tell me how it will done?

This would require VBA as well as knowing what the username is on the computers the two users use when logging in their computers.

Is VBA OK?
Do you know the login usernames of the two users? What are they?