The fabric moves it most. A red can be velvet, a polyester weave, cotton or linen, and each costs differently. The heading comes next: eyelet and wave take 2.5 times the window's width in fabric, pinch pleat 2 times.
With so many fabrics behind one colour, red and other strong colours have no published rate with us. We price them at the free home visit, once you've chosen, with each window priced separately and each part on its own line. The quote holds for 30 days, and how a curtain quote breaks down shows what each line covers.