If a characteristic’s subgroup contain Subgroup Level Control Test violations, the subgroup's color will change to either Red, Purple, or Yellow on the Control Charts.

The levels of severity (from highest to lowest) are:

1. Red
2. Purple
3. Yellow
4. Green
5. Grey  

The cell or subgroup color will always indicate the highest severity level, and will change to the color of the most severe violation. For example, if an Out-of-Control violation, a Mixture/Stratification violation and a Trending violation have occurred in the same characteristic, then the characteristic’s cell will be red. This is because, by default, Out-of-Control violations are regarded as the most severe. However, both rules in violation are recorded within the WinSPC database.

The built-in Subgroup-Level Control Tests are colored as follows:
Red is reserved for 'Out of Control' rule violations.
Purple is reserved  for 'Mixtures' and 'Stratifications' rule violations.
Yellow is reserved for 'Trends' rule violations.
Green indicates no active Control Tests are currently in violation.
Grey indicates there is currently no data for a particular characterisitc within WinSPC.