When fishing a high vis Tenkara fluorocarbon level line, the entire line is a sighter. However a single color can be obscured in specific lighting conditions so I bloodknot Orvis chartreuse-orange-white 0X sighter on the end of my lines that vastly increases line visibility under tricky lighting yet retains stealth with the white at the end in case the line dips under. A tippet ring is tied to the end of the sighter, and I tie 5X & smaller tippet to the ring. This describes exactly how I use a T-line and sighter.
On the other hand Keiryu fishing uses live nymphs as bait with 14'-17'+ rods but short clear 3X fluoro lines and these Japanese Keiryu Yarn Markers are tied on the line above the water. I use the markers on DIY Keiryu clear fluoro lines and T-rods or a K-rod for maximum stealth when "tactical nymphing" with artificial flies. Here's a description of what Keiryu fishing is, what K-lines are, and how to tie the yarn markers on the line so they stay put.
Keiryu Tactical Nymphing, or tactical nymphing with a keiryu rod and line offers some significant advantages over standard Euro-nymphing.
www.tenkarabum.com
The yarn seems to have no effect on casting even when fishing "Tenkara-style" with up to a 17' K-rod and 17' fluorocarbon level line.
At least one of the 4 neon colors will stand out in virtually any lighting to detect where my fly is and any unusual movement that would indicate a strike. Unfortunately TBum, who I've been buying MIJ gear from since 2017, has been out of stock on a lot of items; these yarn markers included. The yarn is similar to egg yarn, but very small diameter strands.
What's the issue with NZ? I have a very inexpensive DIY version of the NZ indicator. $10 for a knit picker, a lifetime supply of clear Pony silicone bead lacing, and using (greased) wispy strands of orange, yellow, and white polypro macramé yarn that I use for tying stones and hoppers cast nicely with a western rod and fly line but didn't float very well when using weighted nymphs. I can't think of why it would not be good as a tight line indicator above the water.