Matrix with columns, be able to adjust major and minor vertical gridlines ...

[MarkB63]

I have a matrix with a date column, and under each date are several values.  I was asked to make the vertical gridlines between dates thicker and darker and leave the vertical lines between the values under each date a little lighter and thinner.  This helps to visually break up the dates better.  There doesn't seem to be an easy way to do this.  Would be a nice feature, unless it already exists and I haven't found it ...