Instead of using alternative dimension; I would suggest creating an island table using the inline load.
Let me explain; let's assume u only have have 2 dimensions; one shown and one alternative; and each time you want to color by the present dimension.
This is how this can be altered:
1) in the script, create an inline table as follow:
load * inline [
2) add this new created Dim field as a filter in ur dashboard.
3) Now in ur chart,
if (DimID=1, YourDimensionA, YourDimensionB)
and color by dimension
Thtis way, every time you make a selection in the dimension you want to show; it would be colored by the selected dimension.
Hope that was clear
If you use the April release (potentially February, I can't test right now) you will have the option of coloring by "relative dimension". Meaning if you pick color by Dimension 1 or 2 in this screenshot then it will always color by that what dimension is used in that position in the chart when the user switches among the alternative ones.
Dimension 1 = Year (X-Axis)
Dimension 2 = Country