I am looking here at the course of current fluctuations and have calculated the RMS values, but somehow it seems strange to me: with the black line there are small fluctuations, but the RMS value is still comparably large with, for example, the blue... The RMS values are: red:0.83mV blue:0.44 green:0.52 black: 0.31mV
RMS includes the mean. If you want a metric for "variation" use the standard deviation instead or subtract the mean first (which is basically the same thing).
For the black curves moves slowly, but it still moves by a good amount. If you want a metric of the "fuzziness" than you can apply a high pass filter first that gets rid of the slow "drift" movemenent.