Have you considered running drip-to-waste from a res of corrected water, and allowing 10% runoff at all times? =Constant mini-flushes.
The color may be from the coco or from your nutes. Some nutes are just really dark, like canna and pureblend. Most likely it's a combination. I'd get in the habit of watering to runoff every time you water, and if that means propping up the pots over a catch-tray, so be it.