蔚(wèi) - azure, luxuriant, flourishing in Mandarin

蔚 (wèi) is a bound character rather than a free-standing word. Its core sense is thick, flourishing growth, and from there it stretches to the rich, saturated blue of a clear sky or a deep sea.

You will meet it almost entirely inside two items. 蔚蓝 is azure, the standard word for a strong sky blue, and 蔚然成风 is a set phrase meaning that a practice has caught on and become the norm. It is also a reasonably common surname, read Wèi.

The trap is treating 蔚 as a colour word you can use on its own. You cannot say 这是蔚的 for this is blue. The ordinary word for blue is 蓝 or 蓝色, and 蔚 only supplies the extra richness inside 蔚蓝. Watch the tone as well: 蔚 is fourth tone wèi, not the second-tone wéi of 为 or the first-tone wēi of 危.