Within each dataset you are able to define a setup of colors used for specific values. An example would be if you used a consistent set of Outcomes that you wanted to represent in the same color on a graph. Another example could be the use of colors to highlight a Likert scale you are using within your Question answers.
To update the colors you will need to navigate to the ‘Data Manager’ option within Analytics studio. Select the Edit on the dataset that contains your referenced field, then explore. Select the dropdown next to the Dataset name to show the Fields panel.