rodgerole was looking for fluorescent yarn sources for the Crappie Candy fly in the chat room last night so I gave him the sites for the yarn I use. I use the Needloft brand of nylon plastic canvas yarns for the Crappie Candy fly for the fluorescent green and yellow chartreuse colors (actual brand name colors I use for these are below). Links below.
http://www.uniekinc.com/yarn.html
Color chart (I use the bright green and bright yellow):
http://www.uniekinc.com/pdf/needloft_yarn_chart.pdf
I can usually find some of these at craft stores or other craft departments of department stores so I don't have to place an order.