You may have seen dogs out and about dressed in an array of yellow paraphernalia! The Yellow Dog Project is an interesting and potentially very useful idea. Basically, if a dog has a yellow collar, harness, lead or has a yellow ribbon tied to the lead then it may indicate that they need space from other dogs/people. This is certainly a real problem for some TCBTS members’ clients!
The campaign was adopted in the UK as Yellowdog (yellowdoguk.co.uk) as a registered charity in 2013 by NarpsUK, a membership organisation for pet sitters and dog walkers. 
There is another site called spacedog.org.uk that is also promoting the idea. Essentially the ‘yellow dog’ scheme has developed as recognition of how difficult it can be for some dogs when other dogs rush up to them.
The yellowdog.co.uk campaign clearly states that dogs might need space for a number of reasons specifically – they maybe: Ill, old, hurt, in season, in training, nervous, have had bad life experiences, the person walking him may be nervous of other dogs or they may be an unknown quantity to new owners. The Spacedog.org.uk site doesn’t appear to give any guidance as to use.
However, the yellowdog website is very clear that it should not be used for dogs known to be aggressive, the website strongly states dogs that bite should be muzzled so the yellow dog is not for dogs known to bite but could be used for dogs that bark and lunge. There are obvious legal implications if the yellow dog is used for dogs with a bite history.
The yellowdog website is not clear as to whether the yellow label applies to dogs when off lead as well as on lead. If you know your dog to be potentially aggressive but let them off lead with a yellow ribbon/bandana on their collar and there is an incident, the yellow label might work against you in court as indicates that you had prior knowledge that this might happen but had not taken steps to mitigate it, whilst if you had your dog on the lead with a yellow label and another dog rushes up and there is an incident then the yellow label might work in your favour in court as it could be seen to have been used appropriately in order to avoid such and incident.
In addition to the ‘Yellow Dog’ scheme these days there are lots of leads, collars harnesses etc in different colours purporting to mean different things and whilst an effective scheme would be massively beneficial for owners and their dogs any scheme needs clarity and unity and also promotion and where better to start than at the vets!
If you see a dog with a 
YELLOW ribbon, bandanna or similar on the leash or on the dog, this is a dog which needs some space. The Yellow Dog campaign believe that by making the Yellow Ribbon an accepted representation throughout the UK that a dog needs space will benefit everyone and make dog walking a more enjoyable experience.