A new name as well as a different colour can be applied to a meter by double-clicking on the meter in the legend:

This will bring up a window where a new name can be set in the Label section and a new colour can be selected from a colour palette.

The change will be applied for all users using the platform. When a report is created it will use the colour that is set at the time of creation. Further changes to name or colour will neither affect the existing report nor future generated reports.