Essentially since using only a legend might not meet criterion 1.4.1 of WCAG, I would suggest considering labels. Having tooltips does mean that technically colour isn't the only means of conveying information, however without hovering that information isn't available. It could be argued both ways but something worth considering.
I think the visuals are there for a guide and can be discussed at Community Of Practice, I don't think its really a part of the template that needs signing off.
You may wish to consider the following: https://analysisfunction.civilservice.gov.uk/support/communicating-analysis/introduction-to-data-visualisation-e-learning/module-9-pie-charts/ https://ons-design.notion.site/Chart-types-e916b8337b064aab9d4ee0db0f56eb86?p=80d01218ca694f429ac7b0255d5c8eee&pm=c
Essentially since using only a legend might not meet criterion 1.4.1 of WCAG, I would suggest considering labels. Having tooltips does mean that technically colour isn't the only means of conveying information, however without hovering that information isn't available. It could be argued both ways but something worth considering.