Some watercolor purists insist you should never use white in a watercolor painting, but I’ve always felt that white has its place. It’s true that diluting is usually the preferred/most uniquely watercolory way to mixing up pale or pastel colors, but pastels made from white paint have a different look – heavier, chalkier, more solid – that is sometimes just what you want.
This post by Leslie Fehling shows how she mixes both kinds of pastels in a travel scrapbook page: making a background with diluted pastels, over which she stencils words in white-mixed pastels. “The tube white gives it the body it needs,” she explains. The ultimate effect is of very similar colors that nonetheless have contrast, yet it’s hard to put your finger on exactly why.
I was reminding of this effect when deciding how to approach this lighthouse reference.

The foreground lighthouse uses essentially the same color palette as the background sky, yet still looks different. At the same time, there is no visible outline or border between the two.
I decided to paint the sky with diluted pinks and blues, and the lighthouse with the same colors mixed with white gouache.

I did this in direct watercolor (no undersketch), which caused all the lines to be a little wonky, but allowed me to avoid having a visible line between between the sky and the lighthouse for that “pink on pink” effect I wanted to achieve.