NZ COLTS SIDE 1953

Backs,Dineen,FB,Cossey,Davison,Lineen,Morris,Walsh,Russell Watt Threequarters .
FIVE eighths Ross Brown,Prain.Thomson
half backs Briscoe,Whitta
forwards Boon,Creighton,Green,Hayes,
Johnston,C.Meads,Pickering,Rowlands
Soper,Tremain,Whineray[captain]Barry,
Many of those were stalwarts of both Provincial and AllBlacks rugby for many years
in the period 1956-71.

Didn't they tour Ceylon (Sri Lanka).

Yes,BUT the NZ Almanack for the year concerned stated Japan/Hong Kong [source for team]

Why were they called the Colts?

Nz Maori were a separate team and Junior All Blacks would be what we would call an A team
today.The Colts would be the equivalent of an Academy side,the Colts were therefore young
uncapped players.The exact reason for the name your guess is a good as mine but young
stallions.?

'Colts' is a common name for academy/age-grade sides.

There's an English Colts Cup for U19 club sides for example.