The title of a web story goes, 婚后的张钧甯尽情散发出知性魅力，穿长款的白衬衫，优雅又有气质 I believe 知性 means smart and intelligent, but does wearing a white blouse make a lady smart? Or if she is in black or other colors, then she looks stupid? What does this phrase really mean?
知性 = intellectual
知性魅力 = intellectual charm
A long white blouse doesn't make a lady smart, it just indicates she doesn't often do physical labor and is well off.
White clothes easily get dirty, long clothes are not convenient to move around in big movements, e.g. physical labor
In the olden time, only rich people got educated. Wearing clean white long clothes implies she is well off, therefore likely educated and refined. Certainly not an uneducated commoner who needs to do hard labor for a living.
The original meaning of 知性 is actually what they said. But the meaning of “知性美” is more commonly used to describe a woman who is showing a comprehensive beauty. Not only is it beautiful in appearance, but also very temperamental and knowledgeable. Both sensual beauty and rational beauty are taken into consideration.