Each account has a display name (what you see in Newton), a sender name (what people see when you email them) and a color. Change them on any device, and the change reaches your other devices too.
Steps
Desktop
Open Settings: press ⌘, on Mac, or Ctrl+, on Windows and Linux.
Go to Accounts and select the account.
Under Profile, click Edit next to Display name or Sender name, type the new name and click Save.
To change the color, click Change next to Account color and pick a color.
iPhone, iPad & Android
Open the menu and tap the Settings gear at the bottom.
Tap Accounts, then tap the account.
Tap Display name or Sender name, type the new name, and tap Save on iPhone and iPad, or the check mark on Android.