I think most people know red and green but other colours are confusing. I was always told white was a stallion, recently read somewhere else that yellow was a stallion but have never heard of it being blue for one! Also never heard of white being for sale.
Seems to be different in the UK to the US and other countries which can make it confusing when you search online.
Saw this of a FB page and as I said one that it would appear different disciplines have different rules on this.
Endurance for example say blue for a stallion and white for a nervous or disabled rider.
I have always used white for a stallion with a white disc on the bridle and have never seen a horse for sale with a ribbon in.