Can you tell me what colour natural discharge from a bitch should be.

Is that when she is in season or not? 

When not in season, nothing but clear, if any at all.  Any permanent discharge even clear would have me bothered!! The inside of the vulva is always moist but an excess would not sound normal to me.

In season, it varies bitch to bitch.  But usually starts with pure red blood, changing gradually from salmon pink to clear at time of ovulation, then usually remaining clear when mated until whelping.

Some bitch's continue red discharge even when ovulating.  But the above is the norm.

She is not in season, she finished six weeks ago. The dischage is stringy and clear, but yesterday i saw some that was a dark greyish sort of colour. I took her to the vet incase of a pyo, the vet scanned her and said there was no sign, but to keep an eye on her. She is very well in herself. Sinse being 6 months old she has always had more discharge than i am happy with. I have had her to the vet plenty of times about this, but all they say is that every dog is different just like people and to stop worrying. Then if i go to the other local vet in my area they just palm me off with antibiotics every time. I am not happy with this, somthing is niggling at me all the time. Do you think there could be a problem with her or am i a paranoid mammy.

Like your vet said I would be keeping a real good eye on her. 

If it is stringy and clear, do you think it is possible that the greyness that you saw was not just diret collecting from her sitting down?  I have had this with bitch's close to whelping, they have had me in panic more than once, when they have sat in some mud and it has clung to the discharge!!!

No I don't think you are being paranoid just concerned which is fine.

Have the vets ever done a blood test to check for high white blood cell count, as this shows if she is harbouring a slight infection.

No they have never done ant blood, they just do the norm, take temp and have a look at her back end. Maybe i should ask for a count doing.
Thanks Lady Dazzle.