Ive had good success with coloring blonde pieces and I've colored an entire piece from blonde to median ash brown which is a very very brown color . I found what works for me is smearing the bottom of the lace with gel (I use Dippity Do gel because it's cheap). I carefully color the hair with a comb and then I get a small artists brush which I buy at the dollar store and use that to get down to the roots.

The first part is actually quite easy but the roots take time. The gel will protect the lace for the most part. When I first started doing this I did get a few spots on the lace but was able to bleach them out. Last couple of times I've done this I haven't gotten anything on the lace so the gel works well.

But I can't emphasize enough that you have to dye the hair shaft right down to the lace or you will have very visible blond roots which looks goofy. I refuse to accept knots at the hairline so going blonde front is the only way for me.

And another thing to keep in mind is that you are going to need to match up your hair color on the piece with a dye. I got a lot of this wrong at the beginning and kept picking the wrong color. Finally got it right when my wife took a hair sample to sallys beauty supply (I'm too Macho a guy to go in there lol) and she matched up my hair sample with the correct color and now it's spot on.