indiscernibly
Definitions
In a manner that is impossible to see, perceive, or distinguish clearly.
In a way that is so slight or subtle as to be unnoticeable.
Examples
The two shades of blue blended together so indiscernibly that it was impossible to tell where one ended and the other began.
He moved through the crowded room almost indiscernibly, avoiding eye contact with everyone he passed.
Synonyms
imperceptibly invisibly faintly obscurely vaguely unnoticeably