Hello, Boyd
Thank you for the very instigating answer. After your clue about Rimbaud, I found a  French site ( with a section named "De couleur en couleur") which  opened up not only Rimbaud´s "Mémoire", but a reference to his synesthaesia... It was  a cleverly arranged program which carried all the various entries into the same poetic theme or even for a single word by Rimbaud ( a little too thorough, almost a spoil-sport ).
We have a common word in Portuguese for the crescent-shape that forms at the edge of any jar filled with liquid and which is connected to the surface tension that creates a drop and establishes a holding limit for the exploration of Transparent Things.
I don´t remember having found it in VN´s various immersions around the "water" theme. I refer to "meniscus". It suddenly occurred to me that  specially useful words ( meniscus has "moon"  in its origin, here as a crescent moon, and not on the "vane" )  left relatively unexplored by VN could yield information about his style, too. 
Just as his insistent probings to describe the colour of grey-green eyes, such as Lolita´s and, perhaps, Ada´s  ( miniver/vair/vert/never/hiver ) which he didn´t appear to find satisfactorily rendered whenever he referred to them...
Jouet de cet oeil d'eau morne, je n'y puis prendre,
ô canot immobile ! oh! bras trop courts ! ni l'une
ni l'autre fleur : ni la jaune qui m'importune,
là ; ni la bleue, amie à l'eau couleur de cendre.
Arthur Rimbaud, Mémoire 
 un I rouge
 A noir, E blanc, I rouge, U vert, O bleu : voyelles,... (Voyelles) 
 des Poèmes rouges
 Blancs, verts, et rouges dioptriques,... (Ce qu'on dit au poète à propos de fleurs)