Expression for the way of dressing to avoid attention

Solution 1:

You would dress inconspicuously.

Solution 2:

Besides already-mentioned inconspicuous, some of the following may apply. I am not suggesting these words specifically mean dressing in a way to avoid attention, but any of them might be used to describe how someone looks who has dressed to not draw attention when among people dressed in a variety of ways. (If everyone else has dressed alike, a person dressed differently will be obvious and memorable, no matter how inconspicuously they meant to dress.)

• bland, “Lacking in taste or vigor”
• nondescript, “Without distinguishing qualities or characteristics; unexceptional”
• mousy, “Quiet, stealthy”
• dowdy, “Plain and unfashionable in style or dress”
• unassuming, “modest and having no pretensions or ostentation”
• innocuous, “Inoffensive; unprovocative; not exceptional”
• forgettable, “Easily forgotten”
• plain, “Ordinary; lacking adornment or ornamentation; unembellished”
• dress down, “To wear casual or informal clothes”
• blend in, “To fit unnoticed into a surrounding. [eg] He disguised himself as a businessman to blend in with the others wearing suits. The aliens adopted human form in order to blend in.”