Actually, it isn't that the old dyes weren't as bright, they could be easily. The real difference is they did fade much more readily than modern dyes and did so rather rapidly being exposed to sun and weather. Vegetable dyes were easily capable of producing brilliant colors.I learned this in conversation with a lady that spins her own wool and weaves blankets and other items. She does occasionally use old dye recipes when she's going for an antique look.