Adding a new marker color can be done on the edit page.  Following the steps:

1. Go to the Edit Page
2. Add a new type or group to your source data (excel) file. (There should already be a column used for this. In the sample 1 data it is the column with the ‘Type‘ header.)
3. Paste (or drag/drop) all the data you want to appear on the map into the main data form.
4. Click ‘Set Options’
5. Go to the ‘Group (marker colors)’ section
6. Show the group markers and change the color for the new group (‘New‘ in the image below).
7. Click ‘Re-Map’