Adjective
not capable of being distinguished or differentiated
Source: WordNetAs the grave closes alike over all whether important or insignificant, so in the roll of Roman magistrates the empty scion of nobility stands undistinguishable by the side of the great statesmen. Theodor Mommsen
the two specimens are actually different from each other but the differences are almost indistinguishable Source: Internet
the twins were indistinguishable Source: Internet
a colorless person quite indistinguishable from the colorless mass of humanity Source: Internet