An entity's name isn't colored in its team's color in the chat if the entity selector does not use the team= argument. This did not happen in 1.15.2.

To reproduce

1. /team add testTeam

2. /team modify testTeam color red

3. /team join testTeam @s

4. /tellraw @a {"selector":"@e[team=testTeam]","color":"green"}

   → Your user name appears in red

5. /tellraw @a {"selector":"@a","color":"green"}

   → Your user name appears in green