which colors should mom be looking for?

Our wedding colors are charcoal, white and navy. The BMs will be wearing this dresses http://www.dhgate.com/new-charcoal-grey-strapless-full-length-chiff... My mom also chose a charcoal dress http://www.inweddingdress.com/style-mo176.html . I'm just worried that it would look weird having the mom in dress that is very similar to the BMs. I don't want her matching my bridesmaids, but also not completely clashing with our color scheme. So with grey BM dresses and navy suits and an ivory dress for me, which colors should mom be looking for?