For many people, the following isn't a difficult task -

Unfortunately,  for the vision impaired (color blind), the challenge is greater -

\While this might not seem all that critical - imagine if instead of "pick the red ball", we were conveying a tornado warning in areas in red and light to moderate rain for areas in brown.

Another example of poor use of color:

The forecast for today is in red  and the forecast for tonight is in green the forecast for tomorrow is in yellow

PARTLY CLOUDY. LOWS NEAR 50. LIGHT AND VARIABLE WIND.
PARTLY CLOUDY. HIGHS IN THE LOWER 80S. SOUTHWEST WIND AROUND 10 MPH.
MOSTLY CLEAR. LOWS IN THE LOWER 50S. LIGHT WIND.