strange behaviour with g.theme object

>g.theme.fg
Uncaught ReferenceError: "fg" is not defined
 at line 1 col 9
g.theme.fg
        ^
>
>g.theme
={ fg: 0, bg: 7, fg2: 1, bg2: 3,
  fgH: 0, bgH: 3, dark: false }
>
>g.theme.bg
=7
>g.theme.fg
Uncaught ReferenceError: "fg" is not defined
 at line 1 col 9
g.theme.fg
        ^
>g.theme.fg2
=1
>g.theme.fgH
Uncaught ReferenceError: "fgH" is not defined
 at line 1 col 9
g.theme.fgH
        ^
>g.theme.bgH
=3
>