I have a Torch Red GT with IUP/Dark Charcoal and white side rocker stripes. I think it looks great. I don't think the color difference is that noticeable since you can't see the inside interior at a distance, and the stripes you can.
The best advice I can give is to go with a stripe color that you think goes with the exterior color the best. Everytime you look at your car, you will see the stripes first. Also, if you ever get the windows tinted, then the interior color will be even less noticeable.
Now if you are trying to attempt a complete color coordination match-the- shoes-with-the-purse thing, then forget what I said!