Table Borders Overlapping / Custom Border Sizes

[Daniel]

Hi all,

I've got a document containing tables with horizontal & vertical
borders.

A group of cells need to be highlighted with a frame around them, so
I've applied a 1.5 thickness blue border around them. However, when the
blue frame crosses horizontal cell borders (also 1.5 thickness, but
grey), these lines overlap the blue border, which doesn't look great.

Now, the only way around this (I can see), is to use a thicker border
for the blue frame - however, I don't seem to be able to set custom
sizes for it's thickness. Therefore, I'm left with either the blue
frame overlapped by the grey lines, or an ultra-thick frame.

Are there any ways around this problem?

Thanks in advance,
Daniel.