In terms of line color, you want a high line visibility, so you can see it, or a low line visibility, so the fish cannot see it.  Perhaps a blend of the two is something we seek. There is also multicolor line that helps us gauge depth. Each brand has line colors rated for visibility. The best way to determine what color is for what purpose is to check the manufacturer specifications on the box. If you’re fishing clear water and want invisibility, you should use fluoro or braid with a long fluoro leader.