Willow is a 7 month old lab and I am wondering if she's come in to season. She has a permament muddy looking deposit round her vulva - not blood coloured- she's had it for about 10 days. We have washed it off - but it's come back. It could obviously just be mud, but I'm beginning to wonder. There's no obvious swelling. With my previous girl there was no mistaking it, but I'm a bit unsure about Willow. Any help gratefully received.

Put the cloth into clean water, if it is blood it is likely to show red if it is mud it will remain brown. However if you are still unsure I would see a vet.

Agree with Nova  on this one

Definitely see a vet,, even if it is just to confirm that it's not a pyo.

what colour is she? only reason I ask is that I have noticed some yellow/ goldens have a kind of staining around there which I've never noticed on my black labs.

dried blood can look quite dark but if it is blood from a season it should be fairly bright red to start with (I think, my bitches have been spayed for ages so sure someone will correct me if my memory's off). Can you try dabbing her vulva with a clean white tissue a couple of times a day, if there is blood you should see it then.
is there any smell at all and is she happy in her self? Obviously it is worth being aware of the possibility of infections if there is a discharge that is not a season. sure it's not but best be careful. :)

With the permanently muddy bits has she been permanently moody or shown signs of forgetting basic training commands as this is often another sign it could be her season!

I can pop round at the weekend or can stop off on the way back from Reading later as can come by your place as will come back via Woodstock if you want ? :-)