there are several types of digital testers, monitors out there, some include PH, TDS, ORP, calcium, salinity, phospahte and nitrate photometers, which are nice but real pricey, i had the same issue as you have with trying to match the colors,i bught a tds and ph meter, i invested in Lamotte and Elos tets kits and they seem to have a much more defined color change scheme, i also invested in a bright desk top light that is very crisp which helps as well. id love to buy all the digital testers, but my wallet said NO!!!!