Verdaccio or Grisaille? Or?

I occasionally paint my cityscapes in this manner because I like it, and also because it's a good selling point. I call it grisaille or verdaccio. Both terms are wrong.

Grisaille is executed entirely in shades of gray, or another neutral color.

Verdaccio is a mixture of black, white, and yellow.

Both sound elegantly mysterious and all, but one ought to know the name of one's own product.  

To summarize: is there a term for a painting that's mostly black-and-white, with just a splash of color somewhere (not necessarily in the logical center of the composition)?

Your painting is a type of 'chiaroscuro':

– (Pronounced: key-ARE-oh-SCURE-oh) an Italian word literally meaning “light dark”. Most usually used to describe a painting created with strong contrasts, such as Caravaggio.

From "Glossary of Oil Painting Terms" at Will Kemp Art School.

An example:

Joseph Wright of Derby, The Orrery

In photography, the term selective colour is used for the effect you describe. Here's a web page found via google with examples of selectively coloured images. Note that like yours, some of the images shown have more than one colour used in an otherwise black and white image.