The dock lines all stay at the dock. Don't know how I created the impression that they do not. The nature of the slip is such that we don't sidetie the boat to the only finger pier, which is very short. Rather, we center the boat in the slip, which is more than twice as wide as the boat, 50% longer than the boat, and delineated mainly by pilings. So, the working end of each of our lines, when cast off, is a relatively long way from the standing lines they are (hopefully) draped across at departure. We use the drape method so that coming back into the slip, you can grab any given line from anywhere along its length. This allows some flexibility in positioning the boat and crew, rather than having to put a crew member exactly abeam of a single point where a given line is hanging.
Because we center the boat between the pilings, we have a total of 10 (white) lines to the boat. 2 bow lines. 2 stern lines. 2 spring lines on aft pilings that run forward. 2 spring lines on the main dock that run aft. (This dock runs perpendicular to the long axis of the boat.) 2 breast lines, one starboard, one port, each running to a piling. Each of these lines remains in the slip when we depart. We do our best to hang them upon departure, as I HATE lines in the water, but that is difficult to do, given the distances involved. The two bow lines and two aft-running springs can get tossed back onto the main dock at departure, but the other 6 lines get draped across more white lines that I have run for just that purpose. So I have a bunch of long white lines hanging from long white lines. Hence my question about color differentiation. I can certainly invest in 10 different colors of line, but I have all the (white) line I could possibly need available to me for no charge. I believe I have considered (and tried) all of the available methods by which lines are "stored" at the slip while we are away.
I would slip the boat differently if I had something to which I could side tie that ran more than 20% of the length of the boat. That would let me eliminate all of the lines on one side of the boat. If another slip were available, I would take it, as it would "fit" the boat better. However, this is a very small private marina, and this is the only currently available slip long enough for my boat. Turnover is non-existent due to the very low rates. At this point, I think I will weave some yarn into the lines, or buy colored line. Thanks for the suggestions.