Yes, yellow tint is perfect color of conditioned electrolyte, which is MORE EFFICIENT then new electrolyte.
The BROWN in solution, during rinsing, is the sludge that normally forms during Brown’s Gas electrolysis. If you let the solution sit still, the sludge will settle and the solution will become clear yellow.
BLACK bits are ozidized construction debris or solidified mineral (from impurities) or plate decomposition. If it is plate decomposition, it only matters if the plates actually decompose. As long as the machine is making gas, it’s OK.