Paracord may darken slightly, but most other cotton or silk cords darken significantly, especially traditional cotton or silk tsukaito. I had burgundy stuff that went black, and even gold that went to such a dark brown it was nearly black. Didn't matter how much or how little resin you applied, the moment the resin came in contact, it was darker.
I saturate the fibers. Completely. The results may not look like it, but I apply resin until the wrap won't take anymore. I'm not just looking to make the handle wrap stiff, I'm looking to make it bulletproof. If you dig way back in my Instagram feed you can see one of my early kwaiken that the customer has beaten and mutilated by using it like a trowel on his property.
Seriously.
Digs rocks out of his gardens and planters with it.
The blade barely looks like a blade, anymore, but the handle is immaculate.