That is a bad designed test, for all the reasons you learn in psychology when talking about experimental test design. Most importantly: How is this thing scored? Imagine you have everything but one block in the right order. Now every element following that false positioned block is one apart from the right position. Are they now wrong as well? Or are they scored as correct as they are in the correct order in itself?…
Most likely you could score with a levenshtein distance. http://en.wikipedia.org/wiki/Levenshtein_distance
Well, it all depends what you want to test. Normally, such an experiment should try to detect which colours when compared can still be distinguished, detecting the smallest notable difference/patterns which don't work for subgroups. I don't see how that could work well with the measurement.
If it really is about the whole row of colours, then the levenshtein distance could indeed work well.