Darks

Here's another take on the tugboat/bridge scene.

What gives this painting its punch is the boldness of the darks.  The hull of the tugboat is a mixed black, not a tube color.  Also, darks don't have to be black; they just have to be dark enough to stand out.  The bridge is a gradation of reds, ochres, blues, and violets. 

The darks work best when contrasted with the white of the paper.  But make sure there are some interesting midtone silhouettes to surround the focal point contrasts.  And just because the silhouette is a midtone, it doesn't mean you can't vary the colors within the shape.  Look at the skyline and you'll see how many colors I sneaked into that solid area.

Be bold with your darks.  They're bound to attract attention!