Item, entity, block, team, and objective display names must be valid JSON text components

Name, CustomName, Lore, and team/objective display names use JSON text components now, just like /tellraw and /title. The format changed a bit, but you can use colors, formatting, and translations now.

1.12

/summon cow ~ ~ ~ {CustomName:"example"}
/team add example Example

1.13+

/summon cow ~ ~ ~ {CustomName:"{\"text\":\"example\"}"}
/team add example "Example"