First off, LME is 20% water so you have to account for that when making substitutions. 1 lb LME = .8 lbs DME.
I use mostly LME (bulk, not canned) and can make some pretty light colored brews, so I don't think that simply switching to dry extract will do it. The biggest impact would be do start using a late addition technique. Basically you start your boil with about half the extract, adding the rest during the last 10 minutes or so of the boil. I prefer LME at this point because the DME gets really clumpy and sticky from the steam. Liquid extract mixes very easily with the near boiling wort. Make sure the heat is OFF when you add the extract - and if you're using an electric burner I'd even move the pot off the burner while adding. It doesn't take much scorching to darken up the batch.
I return it to a boil, add my finishing hops and then start cooling it. If you're doing a partial mash, you can hold off even more of your extract until later. I do most of mine that way, with 4-5 lbs of grain for the PM and I hold all of my extract until the 10 minute mark. It's made a big difference in the color.
You may also notice a little more bittering from your early hops additions because of the lighter gravity boil. Some folks will reduce their bittering additions by 10-20% to compensate - I don't, because I think they end up more like they're intended to be and I consider it an improvement. But it might be something to consider and play around. The later flavor and aroma additions (anything less than 20 minutes pretty much) should not be changed though.
