As a general note, I'd be very wary in historical matters of extrapolating from the UK to the Mediterranean area -- which of itself comprises a number of different countries and cultures, of course, so even giving detail about Italian life might not resemble anything found in Spain. Clothing can vary enormously from place to another, and the lower down the social scale the more differences are likely to appear.
Anyhow, I can't point you to any specific book or website about wedding clothes, but I can waffle on about generalities if it might help.
You're right that (in England, at least) in previous centuries most women would have married in coloured gowns -- a new book I've got about Victorian clothing at the V&A confirms that the fashion for white wedding dresses only started in the mid C18th and even for a long while after that was restricted to the wealthy. By the early C19th the less well-off are choosing colours like dove grey or fawn or light blue, which were more practical and could be worn on other occasions, and I suspect that such colours -- comparatively sober without being sombre -- were prevalent in the previous couple of centuries. (But of course, by then England was a Protestant country, which had an effect on what was worn.)
If you're looking at the artisan class, for the most part they are likely to ape the current fashions of the wealthy -- sumptuary laws permitting -- so if you have some idea of upper class wedding dress fashion I'd suggest you use that as a basis and dial down on the quality of the materials used, so eg linen not silk, rabbit not sable. Hair coverings are going to be one way of distinguishing between the young bride and a widow, as are the colours, with fresher, slightly brighter colours for the younger girl.
Whether they make the clothes themselves or have them made depends on their skills, the time available, their wealth, and the availability of seamstresses locally. I suspect, though, that many brides wouldn't go to any great lengths or expense but instead they would marry in their best gowns, perhaps slightly tarted up for the wedding. If this is set in a kind of Renaissance, then you've no doubt got sleeves tied onto the bodice, not set into it. If that's the case they might well have new sleeves made in a richer, more sumptuous material, perhaps with slashing so that the fabric of a new underdress/shift/smock beneath can be pulled through and puffed. Similarly an old dress could be refashioned by a gore to give a new panel of more expensive material at the front, or lace could be used to decorate the neck.
Are the characters marrying in a religious ceremony in a church or similar? If so, then you'll have to take account of what restrictions are placed on women generally eg hair coverings might be compulsory and fashionable low cut dresses might not be allowed -- though the latter could be disguised with a scarf or the equivalent of a fichu. You also need to take into account the climate and season when deciding on how to dress them, and of course, you must think of their characters -- in every society there will be some who don't adhere to the usual forms of dress for one reason or another, so if these people are quite self-sufficient and don't care what the neighbours think they might not go to any trouble at all when it comes to what they wear at their weddings.
Frankly, though, despite the fact I'm very interested in historical clothing, and I've ensured I know exactly how my characters are dressed in all my WiPs, unless it's a plot point I don't see you need to give anything more than a basic description of what the two women are wearing. No one is going to "see" precisely what you describe, even if you go into detail, few readers are going to care one way or another, and fewer yet are going to have enough historical knowledge to question what you've done, and since it's fantasy even I'd give some latitude for artistic licence!
