The other day a friend of mine gave me some 000 level fly line... Running line I think they call it.
He also had some 10# Running line in Flu. Yellow. We tied up some 14 foot lines for out 13 foot rods and went to the lake.
Worked just fine. he also had some 15# weight Running Line which I found a little heavy for my rod.
I like the tapered braided Tenkara lines too. What ever line you use... I agree with the high visibility guys. (I can see the line.)
I think you'll find that different lines work under different fishing situations.
Wind, sunny or deep shade, type of rod, weight or type fly, how and where you like to fish.
Just keep trying different stuff till you find something you like. That's part of the fun of Tenkara.