If someone blends into a particular group or situation, they seem to belong there, because their appearance or behaviour is similar to that of the other people involved. It must have reinforced my determination to blend into my surroundings She felt she would blend in nicely He blended in with the crowd at the art sale
If something blends into the background, it is so similar to the background that it is difficult to see or hear it separately. The toad had changed its colour to blend in with its new environment. a continuous pale neutral grey, almost blending into the sky