adjective. Not readily noticeable.

Not conspicuous or readily discernible; not to be easily perceived by the sight; so small or unobtrusive as readily to escape notice.

adjective. Not conspicuous or noticeable; hardly discernible.

adjective. Not prominent or easily noticeable

adjective. not prominent or readily noticeable

"We pranked a co-worker that none of us could stand by smearing sour cream in inconspicuous areas on and around his desk, (inside the mouthpiece of his telephone, on his pens, etc)."

conspicuous  

obscure  unnoticeable  

obscure  unnoticeable  

inconspicuousness  

blameless  defenseless  drab  featureless  homespun  

blear  bleared  bleary  blurred  blurry