Constructor initializer lists can be all on one line or with subsequent lines indented four spaces.

team_c++_style_guide_constructor_initializer_lists.h

// When it all fits on one line:
MyClass::MyClass(int var) : some_var_(var), some_other_var_(var + 1) {}

// When it requires multiple lines, indent 4 spaces, putting the colon on
// the first initializer line:
MyClass::MyClass(int var)
    : some_var_(var),             // 4 space indent
      some_other_var_(var + 1) {  // lined up
    ...
    DoSomething();
    ...
}