Not too bad and it also hurts the eyes, but if it were to be used as the default, the opacity of the orange background would be reduced. Though the background of the forum is a kind of sky blue which relates to light-background and it makes texts on black readable.
Same light color background, replacing blue padding backgrounds with orange would be fine.

Apart from eyes strain, another disadvantage of the orange background you posted above is that, it will interfer with the color of signature designs and render it unattractive.