Lots of food for thought, here. I was leaning towards the lighter coloured one. I guess my main concern is that the jacket would be too warm and therefore not useful. I do travel with just a carryon (and wear my jacket on the plane), so I don't want to bring anything that wouldn't be useful. My big concern is the lining. I find polyester linings can feel hot, as they tend not to be all that breathable.
Both jackets are water repellent and washable, and we'll be staying in apartments, except in Madrid, so washing, if I have to, isn't a concern, and the lighter coloured jacket is more of a light grey/mushroom colour and not as white as it looks in the pic.
I did bring a similar type of jacket last July to East Central Europe, and there were two days--one in Vienna and one in Munich--that were cold and rainy, so I was very glad to have it. The reason I don't want to use that one again is it is a little too short. I tend to wear longer, tunic-style tops that come down to the tops of my thighs, and I thought it looked funny to wear a jacket that let my shirts hang out the bottom. I do have a lighter weight Eddie Bauer jacket with a hood that zips into the collar, but, to me, it's more of a hiking-in-the-mountains jacket than a touring-around-a-city jacket, if you KWIM. It is brightly coloured and very casual-looking, so not as versatile.
I do bring a large chiffon scarf or two that can double as a wrap, but those wouldn't do on a rainy or blustery day. Pashminas aren't really my style, so I don't think I'd use them after the trip. I'd rather spend my money on something I'd use at home, also, and not just on the trip. (Both jackets are on sale, so I don't mind the purchase. The light one would cost me $78 with a discount card and the remainder on a gift card I have, and the navy one is on sale for $55.)
I'm just not clear on May in that part of the world. Where I live, it can be like summer in May, or it can snow, sometimes both on the same day. I understand that Lisbon and Madrid, at least, can also be variable in May (although probably without the snow. LOL).
I know that I do want to bring a jacket. I'm just not sure about which jacket.