Re: Perch pattern black stripes
Yup use water proof markers
For black barring for a perch fly a Black Sharpie would work. (I also use Red Sharpies for gills on epoxy flies.) You can find them in most stationery and the school supplies aisle in big grocery stores.
If you're looking for an assortment of colors and shades
BicMark has an inexpensive assortment of 36 colors for 12 bucks or so at many discount stores.
And if you're looking for a wide variety of colors then look for an arts/crafts store that carries Pantone Pens