@drac my understanding of the colours is it does the same as the eye patch. As each eye sees colours slightly differently using a coloured transparency means the signal from one of your eyes is perceived as stronger than the other and the brain pays more attention to it, stabilizing the words on the page (this is the science as I understand it!)
I was on a trial out of great ormond street (this was 30+ years ago). They tested which eye was dominate and out of 20 times, 10 times it was left and 10 times my right. I then wore a patch over my left eye for a couple of hours a day whilst reading/doing homework etc. After I think it was about a year I was retested and my right eye had become dominate 60/40.
Like the coloured sheets we were told it won’t work for everyone but I know it made a real difference to my learning.