Aligning Objects to Center of Grid

Hi everyone,

I am trying to figure out why my shapes (any shape at all) won't align specifically to the darker grey vertical lines on the grid. 
As you can see in the picture the purple alignment lines (which I use as a guide to make sure all of my objects are aligned in the center) seem to never be on the dark grey vertical grid line instead the shape aligns off one of the lighter grey grid lines.

I don't quite understand the point of having a grid if I cant align my shapes to the more obvious darker lines? Is there some way that I can make this easier.
When I click the "center" button (the second button of six) under Align it does the same thing.

Really appreciate your help with this! Thank you and have a lovely day.
🙂