If Sir Walter was indeed wearing 'black ribbons' as a token of mourning for his heir's wife, I think this would have meant a black armband.

There are several articles out there on the Web about Regency mourning customs, which were not as strict as during the Victorian period.. It seems that the customs regarding mourning dress applied mainly to women, since male dress of the period was in any case pretty sombre, with dark coloured coats (jackets) the norm.

The page linked below is unusual in that it cites contemporary sources for the rules (not laws!) for male mourning attire during the Regency.