light-and-salt

Or we can make the rule a bit more specific like ``` hard(no_stack_with_bar_area_discrete_color,E) :- mark(bar;area), channel(E,color), discrete(E), field(E,F), field(EX,FX), field(EY, FY), F != FX, F != FY, not stack(_). ```...

`F != FX, F != FY,` is my ugly way of saying that the color field is not the same as the x field and it's also not the same...

Right, so it should be ``` hard(no_stack_with_bar_area_discrete_color,E) :- mark(bar;area), channel(E,color), discrete(E), not redundant_color(E), not stack(_). redundant_color(E) :- channel(E,color), field(E,F), channel(EX, x), field(EX,FX), F = FX. redundant_color(E) :- channel(E,color), field(E,F), channel(EY,...

yup! looks good to me!

Just noticed [this vega example](https://vega.github.io/editor/#/examples/vega/distortion-comparison) picks color like below.  Not saying this is the way to go for Voyager, but I want to mark this example.

My problem is solved on StackOverflow: http://stackoverflow.com/q/34820111/1270459

> Hi, I have this problem currently (though I am using different contexts on the same route), don't suppose you managed to find a solution? No... I didn't find a...