Cecil, as Electrathon said, you should undo a few laces at the beginning so that your joint between the two are cleaner. I can see by the pic that the joint of the two laces is not exact, as the one lace is actually going over, not under the next one.
As too the darkening, what I do some times, is to use an acrylic clear coat where I want to block-out. Then after I've stained or dyed, I'll wash the acrylic away, and then I can darken the area I want.
Ken