They come only complete with ends, it's very difficult to get them onto the fittings (I think they are heated and machine installed on the barbs).

I think the are clear to permit you to see the fuel (or lack of it as bubbles) moving in the line.

I'd not replace them unless the leak.

You can cut them off and use standard diesel fuel line with hose clamps instead.

This works with gasoline lines on K-Jet fuel systems as well -- some lines aren't readily available. I did this on the TE, gets better milage now without the drip, to say nothing of the fire hazard....

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!