For years, around 1995 to 2008 ish I used Daiwa Sensor in brown, on various lakes and reservoirs. From 2008 or 2009 I started using Gardner Pro, normally light as the waters I fish are normally clear. I mentioned above about leaders if I was casting long distances, Drennan Greased Weasel in grey, Amnesia in clear or black has never been an issue.
I've watched carp spooking around lines, and it's usually tight lines. I've also seen them spook off fluorocarbon mainlines, whether it was the shadow on the lakebed or possibly the vibration (?) I don't know.
Unless your rod tips are mega high, and fishing super tight line, at anything above 40metres the line near the end tackle is likely to be on the lakebed, unless you have 'raised' features like gravel bars to hold it up.
I've not been one for 'fish protection' * as with monofilament or copolymer lines, I think the line rarely damages the fish. Braided mainline/leaders and leadcore however I do think can cause cuts, grazes and scarring if they rub.
I occasionally fish with tubing, but it is a rarity, and it is for the real name, anti-tangle tubing, to prevent braided hooklinks tangling around the mainline.
I normally fish with my rod tips as low as possible, often underwater, to keep the line down, and if I can with running leads and slack lines.
*Fish protection, that doesn't mean I don't think they deserve protection, but just that the line is not at fault.
We normally fish rig rigs or floater fishing with naked mainline, and hook carp on tench gear, or accidentally while float fishing or ledgering for other species.
Camouflaging weights, (sinkers), is it necessary? On my current water the lead in many swims is in the silt. Just dropping a lead in the margins, it is a job to find it. I have lost a few that I have seen fall off the link clip, the run ring fell after a pike bite-off, or where I dropped the blooming thing. I do paint and coat my leads, with a hard varnish, but I think its more a confidence thing camouflaging than a requirement.
The fish I had this week and subsequent casts, I had to pull the lead free from the silt!