Table with space between cells

Hello, 

I need to configure a table with space between cells.

So far I made this:

But as you can see - if you look closely - there are traces of - in this case - blue lines that cross the spaces between cells. 
It's very anoying and it defeats part of the design idea. 

I understand that this is part of the filling color of the cell that somehow appears even thought that part is covered by grey space.  

In the case of white cells it's not so obvious because the white and grey background melt better. 

I cannot change the header fill color to other than this blue because of requirements. 

Do you know an alternative way to achieve this kind of design? Or a way to solve this little issue?

Thanks a lot