is it ok for the bitch to eat the placenta.

A few are fine. Too many will give her the runs. Ideally you need to know she's expelled them all, so make sure there's been one for each puppy.

thanks for your help i have posted another post asking about discharge can you help

In the wild they would eat them all as it would be a major source of nutrition for the first few days when the bitch could not get food for herself.  The hormones also help with the let down of milk and to help the uterus contract.

I have never had any option but to let my girls have them all, as they are usually too quick for me to remove any if I had wished.  I have never had them have the squits as a result.

If the litter is fairly small (4 or 5 pups) there shouldn't be a problem. The placentas from a litter of 10+ (not uncommon in my breed) can cause horrendous diarrhoea.

would the colour be greeny black

My bitch ate all 6 of the placentas, there was NO WAY I was going to get to them before her and I thought it best to let nature take it's course. She didn't have the runs either but her poo was rather black ;-)

surely you can tell which body part the discharge is coming from, her bum or her vulva?!

yes the discharge is greeny black.