Paneling and Trim - corner trim: how wide to buy?

I have a darker blue room I'm painting and will have 3.5 inch flat crown but a friend suggested putting white 'corner trim' (- runs floor to ceiling and i assume that's what it's called? ) in each corner to both brighten up the room and also to make it look better. I agreed with this but was wondering if there's a best size for the trim?

also in one area it will be just 6 inches from a door but i guess that cant be helped.

Every time you add something you add "weight" to the room. Are the walls sheetrocked? I would be reluctant to add any corner molding unless there is a reason for it to be there. However, if you think it would look good as an accent, by all means, go for it. The smaller the better, so I probably wouldn't go over 3/4" stuff. It will run from the top of your baseboard to the bottom of your crown, just for info.

it's plaster. Do you mean literally pounds and ounces or do you just mean 'clutter'. I'm pretty sure you mean clutter because that small a piece of wood probably doesnt even weigh a pound :)

and i wouldnt even consider it except the room really will be dark when i'm done and i was thinking a tad of brightness would be nice. I dont mind being dark per se but just have a vision of this trim and woodwork being 'outstanding' when i figure out what color white to make it.I guess ill have to buy a sample piece and see how it looks

Here's just my 2 cents. Only you can decide whether you think it will look good, but there are a couple of things to think about. The actual corners of the room will most likely not be sharp. What I mean is that they will be slightly rounded. Take a close look at them and you'll see what I mean. Now the molding you buy will be sharp. What I'm guessing you would have to do is cut off that sharp corner a little bit so it would fit into the rounded corner of the walls. Trim like that is usually used when you have paneling to hide the corner. The edges of the paneling will create a sharp corner that the molding will fiot into. Also, if the wall angles are more than 90 degrees you will have a problem with the molding on one wall or the other. You will have a slight gap.

Not trying to burst your bubble here. Just things I thought of as I was thinking about what you want to do.

thats what i need..point out things i need to be aware of..until i brought a test piece of crown home, i had no idea i had to check and make sure it was perfectly straight...i turned it upside down and there was a gap so i need to return it.

I have no clue how corner stuff will look so yes i need to bring a piece home and see how it fits.

regarding slight gaps, isnt that what caulk or spackle are for ;)