Flying unofficial flags in England can, in theory, result in fines since they can be considered as advertising and so require a licence. But It is quite common to see all types of unofficial flags, often carrying a message, on display in public places without much obvious legal action.
The Yorkshire-wide design registered by the Yorkshire Ridings Society - the single rose on plain blue - is the one commonly available. It is the one used at almost all official events. Despite being registered the colours do seem to vary significantly in shade - probably because exact Pantone references are hard to find (or non existent?).
However there was at least one different design for Yorkshire - a rose and sun on the St George’s cross; shown here as two slight variations. Despite not being officially recognised this flag had more going for it - incorporating both the central design elements of the Yorkshire coat of arms and the flag of England.
Then later this same design of flag became the winning entry in a competition for a new West Riding flag. And was officially registered at the Flag Institute on 23 May 2013. In addition official flags for the North Riding and East Riding were selected and all are now commercially available. South Yorkshire is not a traditional riding and is treated in the same way as regions such as Humberside.
But despite this recent activity and official recognition there are various earlier - and unofficial - designs that appear in shops and on the Internet.