Water is polar solvent but CCl4 is non-polar solvent, though both have Br decolourised, but the white ppt is only observed if aqueous Br is used.

To make Tham KY's answer more detailed:

By using a polar solvent e.g. water, a stronger dipole is induced in Br-Br, resulting in more/stronger electrophile Br+, which is much more susceptible to attack by the benzene ring. Hence a white ppt of tribromophenylamine can be obtained.

In the case of CCl4, because it is non-polar, the effects of electrophilic substitution are less pronounced, resulting in only mono-substitution (instead of tri), where no white ppt is observed.

But isnt the decolourisation sufficient? Where is there a need for white ppt?

Simple alkenes can decolourise br too...