A palette can look harmonious as a row of swatches while becoming confusing in an actual composition. The missing step is assigning the colors to recognizable roles.

Choose which color supports the background, which carries ordinary text, and which marks emphasis. Check the pairings in use rather than judging each swatch alone. A color for decoration may not be appropriate for readable text.

Apply the palette to a small realistic piece and look for competing accents. Keep emphasis focused, and provide other cues when color conveys meaning. The useful palette is the one that helps the viewer understand the work.

A few starting points
  1. Assign colors to clear roles.
  2. Check actual foreground and background pairs.
  3. Keep emphasis focused on the intended detail.

An example to consider.

Consider a poster with several equally bright elements. Reserving emphasis for the main message can make a smaller palette more expressive.

Put it in perspective.

Review what the audience encounters first. The entry point of a composition can decide whether the rest of the idea has room to be understood.

Follow a related question

Write the next action before leaving.

Leave a note for your return

Review focus and busy states.

A button has more than one state

Keep learning

Related background to continue exploring this subject.

MDN: image file formats W3C: accessible image tutorials
Make room for ideas