Colors are an important consideration in any operation interface. Color can be used to signal changing values or conditions, to provide an indication of the purpose of an object, or to warn. The color red typically indicates an "off" or "stopped" state, a "stop" action, an urgent warning, or a negative condition. The color green provides the opposite effect, indicating an "on" or "started" state, a "start" action, or a positive condition. Because these colors are universal, they will be immediately understandable by operators.
Throughout the application, we will use the color red to indicate an "off" or "stopped" state and green to indicate an "on" or "started" state.
Alarm Indicators
When planning our tutorial application, we must also consider alarm colors. In addition to being associated with off or on states, the colors red and green are also associated with urgent and normal conditions; therefore we will use red to indicate urgent alarm conditions, and green to indicate normal alarm conditions. Yellow is typically associated with a cautionary condition.