"plain outfit" is a correct and usable phrase in written English.
It refers to a simple and understated clothing ensemble. You can use it in a sentence when describing someone's clothing or when giving instructions on what to wear for a specific occasion. Example: She decided to wear a plain outfit of a white t-shirt and jeans to the party. or For the job interview, it is best to stick to a plain outfit, such as a black suit and a neutral-colored blouse.
If you're just after a shot of colour to add va-va-voom to a plain outfit then there are plenty of great accessories at the moment.
Bingbing's bag gives her all-black ensemble the right punch to make her plain outfit look very fashion-forward.
For her big day, Nicki chooses a flattering but rather plain outfit: dark pants, leather boots, a coordinating cobalt sweater and wool coat and a white scarf to top it off.
Wear colored jewelry with a plain outfit.
You can jazz up any seemingly plain outfit.
Add zest to a plain outfit by wearing brighter shoes.
That gave a prim sexuality and a dash of wit — especially when the gamut of patterned and plain outfits were printed in miniature across a single dress.
The participating families were lower-middle-class; the mothers were wearing plain outfits and carrying their beautiful babies (ages 6 months to 4 years) dressed in tiny fluffy dresses.
The four players intent on a pair of xylophones in the first part of "Drumming" -- Bob Becker, Russell Hartenberger, James Preiss and Mr. Reich himself -- were there when the music was new nearly three decades ago, wearing similar plain outfits of white shirts and dark pants.
There, the young people, holed up in the store, essentially play house, using the fancy sound systems on display to listen to pop music (and repeat celebrity-news banalities about it), exchange their plain outfits for designer clothing, bathe in a retro bathtub, take jewelry, don makeup, crash on fancy furniture, and luxuriate in the wide-open spaces of the full-block-size building.
Perhaps unsurprisingly, my favourite item of my mum's was the plainest outfit she wore: a black crepe wraparound Ossie Clark dress.
