Azure
Azure is the heraldic tincture for blue. It is one of the five main colours in heraldry, along with Gules, Vert, Sable and Purpure. In black and white engravings Azure is shown with horizontal lines. Heraldry has no fixed shade, so any clear blue counts.
The royal arms of France are the classic Azure coat. France Ancient was blue strewn with gold fleurs-de-lis, and from about 1376 France Modern cut them down to three: Azure, three fleurs-de-lis Or. A lighter sky blue, bleu celeste, shows up in some modern grants, but it is a separate tincture and not the same as Azure.
The coat of arms maker opens with an Azure field and a gold lion, so you can see the pairing straight away. Click the field to keep it or switch it. Azure works best with a metal on top, either Or or Argent.