I have several students with whom I've used various filters, with varying results (only one "dramatic" result, but many positive results in terms of improving stamina and fluency). My favorite actually doesn't have color. It is translucent grey with a clear window for one line of text. Most of my students liked this one because it isolated the line they were reading (making it jump out)but didn't hide the line below it, so the return sweep is easier and reading is more fluent. I had one student who liked that format, but preferred the color yellow, so he would slide a wide yellow filter underneath it. A recent modification I used was to take one of the slim strips, cut the solid border off of the top, and then cut the size to cover only 4-6 words at a time. This forces the reader to actively "sweep" left to right as they read. It was fantastic for a student who seemed to be seeing and trying to process the entire sentence at once. Once we began using that accomodation, he became much more fluent. It occurs to me that colored tabs that are on page dividers might word for this. The tinting isn't exact, but it might be a cheap/easy way to test color preferences. Also, if you have a teacher supply shop in the area you can probably find these kinds of tools and save yourself shipping costs
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