Royal blue wedding dress

The Oxford English Dictionary defines "royal blue" as "a deep vivid blue", while the Cambridge English Dictionary defined it as "a strong, bright blue colour", and Collins defines it as "a deep blue colour". US dictionaries give it as further towards purple, e. g. "a deep, vivid reddish or purplish blue" (Webster’s New World College Dictionary) or "a vivid purplish blue" (Merriam-Webster).