Indicators are weak acids or bases which change color depending on the pH of the solution. Because they have such vivid color changes, only small amounts of indicators must be added to a solution which also limits any side effects they might have on the reaction being observed.
At pH values less than 3.1, methyl orange is red and a pH values greater than 4.4, it will be yellow. In the range between 3.1 and 4.4, you will see a mixture of the red and yellow colors such that in the middle of this range, the solution will appear to be orange.
Since acidic solutions have low pH values, it will be red and transition to orange and yellow as the acidity of the solution decreases. In basic solutions, it will be yellow as well as in neutral solutions because the pH of a neutral solution is approximately 7 and falls after the color change of methyl orange.