Hi,
We can keep color by category using value color(column property > value color)
But, In the case of multiple Y(multiple columns), the situation is slightly different.
In this case, color must be specified in legend to keep original color.
Nevertheless, the Legend setting option is also only available when there are more than two variables.
If we remove one in two variables, the color is not maintained.

I think that this is functional limitation. So, I want to suggest below
1) We need to keep the color by variables in case of multiple Ys
2) Or need easier methods using legend setting to keep the color.
The more variables, the more inconvenient.
Of course, we could use tables > stack. But I think that ‘Stack’ is a another option.
Thanks
Ikju