There is no need for a blouse to look austere just for you to fit in at an otherwise stuffy work environment. You probably admire the dedication and professionalism of your coworkers, but it’s okay to draw the line at boring monochromatic three-piece suits.
Wear sleeveless versions of feather light polka dot button downs with a fitted blazer and pair ones in long sleeves with a black pencil skirt. On your way out of the office, in anticipation of a fun night, undo the first few buttons and let your hair down. Swap a big leather briefcase for a bright oversized clutch. You will look successful, trendy, and like you know how to let loose.