An objective legend is a theme that ties in together your roadmap cards. These may be strategic areas of interest, or a particular goal you wish to achieve across your account.
Objective legends are set on an account basis - so whatever legend you set for one product will be set for all products. There are a total of 9 available for you to work with.
To edit your objective legend, simply click on 'Show objectives legend' on any of your roadmaps. This will toggle the legend and allow you to name each color. Just click and start typing!
Once your legend has been set, you can then use the filters to filter down on colors/objectives of interest.