To get markers on all the points, use the drop down menu next to Color on the Marks card and select the middle option next to Markers. To add a point to both ends of the line, create a calculated field similar to the following:
if first()=0 or last()=0 then sum(Sales) end
Then, create a dual axis with Sales and the above calculation. Change the mark type for the calculation to be a Circle. Right click on the axis and select Synchronize Axes...To change the colors based on the value, another calculation similar to the following can be created and placed on the color shelf:
if first()=0 and sum(Sales)>0 then 'green'
elseif last()=0 and sum(Sales)>0 then 'green'
elseif last()=0 and sum(Sales)<0 then 'red'
elseif first()=0 and sum(Sales)<0 then 'red'
Hope this helps!
Thanks, Tracy! Works like a charm (though I wish I didn't have to sacrifice my secondary axis).