In Chinese culture, bright colors are often associated with positive and auspicious feelings. Unlike in some Western contexts where bright colors can sometimes be seen as gaudy, in China, they are frequently embraced for celebrations and important events. The color red (红色 - hóngsè), in particular, is the epitome of a 鲜艳 color and symbolizes luck, joy, and prosperity. During Chinese New Year, you will see 鲜艳的红色 everywhere—in lanterns, couplets, and clothing. This cultural preference for vibrant, lively colors makes 鲜艳 a very common and positive descriptive word. A useful comparison for English speakers is the word “vibrant.” In English, “vibrant” is versatile; you can describe a “vibrant city,” a “vibrant personality,” or a “vibrant economy.” However, 鲜艳 is much more specific and is used almost exclusively for colors. You cannot describe a personality or a city as 鲜艳. This specificity is key to using the word correctly. It's about visual brightness, not metaphorical energy.
鲜艳 is a common, everyday word used in both spoken and written Chinese. It's neither overly formal nor slang.