Hi Nat Trap
While the amount of light a VFT receives can affect the coloring of the plant and trap, it isn't necessarily the definitive factor. Some VFTs won't get real pink or red no matter how much sun they get. That depends on the genetics of the plant. However an east window should be ok for your plants. An eastern exposure isn't real strong sunlight and the amount of hours is limited (err...unless you live somewhere exotic... I don't know where you live.). In fact your plants might do better with a little more sunlight than that.
What you need to be concerned about with a terrarium and direct sun, is that the temperature doesn't build up inside and get too hot. Also you need good air circulation so the inside doesn't stay too warm and wet which encourages mold and fungus.
As long as you watch the temps and air circulation, I don't see any reason why your terrarium can't go in your window.
Good luck!
Suzanne