Different colors for a single line in a multiline line chart

Hi, I would like to create a line chart as follows: 

I have created two measurements for actual values (colors) and forecast (grey): 

actual = IF('Table'[Month Number]<= 6, [Sales], BLANK())

forecast = IF('Table'[Month Number]>= 6, [Sales], BLANK())

But I also want to have a line per category (4 lines, part color, part grey). I cannot add a field as a legend, when I have two measures on Y axis. How can I achieve this?