Hi there and welcome, Do you have a photo of the weed? You can read about how to post photos on the site here: http://www.gardenstew.com/about4115.html
That is Purple Dead Nettle (Lamium purpureum). The easiest way to get rid of it would be to just pull them up. Also, the use of a broadleaf weed killer would probably get rid of it.
I usually pull them out too, very shallow roots... seems like it goes away once the grass kicks in. I always wondered what it is -- now I've googled it. This link says it's edible: http://www.naturesherbal.com/Purple_Dead_Nettle.htm