I am happy to say that in the process of reading my way through Federico Garcia Lorca: Three Tragedies (containing Blood Wedding, Yerma, and The House of Bernarda Alba -- all of which, I believe, are subtitled Hoo Boy But These Women Are Crazy), I have managed to reassemble what I believe is a reasonably full decoding of Lorca's symbolism:
Black = Death
Green = Death
Silver = Death
Still water = Death
Running water = Death
Sea water = Death
Moon = Death
Flowers (all) = Death
Anything Else That Happens to Come Up in the Course of a Work by Federico Garcia Lorca = Death
I don't worry about that last one too much, though, since you almost never encounter it.
Srsly. I like Lorca's stuff, find it completely and weirdly compelling, but... yeah. Death death death death death.
P.S. I miss my high school Spanish teacher. Death got a hold of her too. Last year, I guess, and I hadn't seen her in eight or nine years... but it still makes me sad. I hope death has been kinder to her than it is to the characters in Lorca's plays and poems.