Arthurian Tropes on Epic Quests
Dawnish characters come from the equivalent of the eastern midlands of the Empire - while the climate and terrain can be extreme in some regions, it's mostly a pleasant and temperate land.
They like bright colours and rich fabrics, brocade, and stylised heraldic animal motifs. Dawn has a class system - Nobles are expected to look rich and like they don't do a lot of manual labour outside of sports and martial pursuits. Yeofolk are the working class, and their costumes will be a little simpler and more practical.
For the core Dawnish look, think about a renaissance fair or an 80's swords and sorcery movie - that's the general direction you're looking in.
Summer Meadow and Jewel Colours
You're looking for the colours of summer. Deep sky blues, bright sunflower yellows, striking reds, rich purples and green grass, along with silver and gold metallics, in brocade, velvet and other rich fabrics.