For me it was very sensitive to even one red pixel from a sign not being selected

It's also incorrect: there is the back of a stop sign visible on the left of the picture but you must not select this to pass the level.

Par for the course with these captcha-like tests though.

	▲	jimmydddd 3 days ago \| parent [-]
		Thanks. That was it. You are NOT supposed to select any part of the back of the stop sign to the left of the picture.