Navy blue, with a navy tourie.
The military glengarry has become the standard headgear for pipe bands, and Reelpipes.com offers this high-quality, Made in Scotland option from St. Kilda and RG Hardie. These are excellent bonnets that hold their shape in all weathers and don't fall apart, stiffen or discolour.
Available in a full range of sizes. See the attached chart for sizing. Hat size can be determined by taking a measurement around the head where the glengarry will sit.