Mean of input based on acf of filtered output
Yes. Mathematically, the limiting value of the autocorrelation function $R_X(\tau)$ of a wide-sense-stationary process is $$\lim_{\tau\to\infty}R_X(\tau) = \lim_{\tau\to-\infty}R_X(\tau) = \mu_X^2$$ where $\mu_X$ is the mean of the process. So it is not too surprising that res1 and res2 have identical shapes but res2 is shifted upwards in comparison to res1 and the above equation tells you how much the shift is.