THING varname
:varname

Outputs the value of the variable whose name is the input word. If there is more than one such variable, the innermost local variable of that name is chosen.

The colon notation for showing variables is an abbreviation for

THING "

So :foo is the same as (THING "foo).

MAKE "foo [Hello how are you]
SHOW THING "foo
[Hello how are you]
SHOW :foo
[Hello how are you]