Adding multiple line series to one chart

I dont know if I used the right terminology in the title but, i am trying to create a milestone graph - using an incremental y scale (going up in 1s) , dates along the x axis and the milestones plotted at 0.5, 1.5, 2.5, 3.5.....etc

Problem is I need to colour each point differently, for example missed milestones (dates in the past) as red, others in green , some amber, etc. I created a table with 3 columns, red, amber, green - there are dates for each point(0.5,1.5,2.5....) but you cant have a date against multiple points i.e if there is a date in the red column, there wont be one in the green column, instead it will be #n/a.

So, when I select the Red and the position columns i create a normal line graph, now i want to select the amber column and the position column , copy it and paste special over original graph as a new series, but this just seems to repeat all the points generated by selecting the red column. If i create a separate graph using amber and position then it looks as i expect with different points plotted to the red graph.

Any help appreciated!

attached the sheet - 3 graphs on there, 1 shows the red milestones, 1 amber and the other is an attempt at combining the two but as you can see it just seems to have put the same points on again even though i've selected a different data source

cool! thanks very much