We present multiband photometric observations of nine Centaurs .
Five of the targets are known active Centaurs ( 167P/CINEOS , 174P/Echeclus , P/2008 CL94 , P/2011 S1 , and C/2012 Q1 ) , and the other four are inactive Centaurs belonging to the redder of the two known color subpopulations ( 83982 Crantor , 121725 Aphidas , 250112 2002 KY14 , and 281371 2008 FC76 ) .
We measure the optical colors of eight targets and carry out a search for cometary activity .
In addition to the four inactive Centaurs , three of the five active Centaurs showed no signs of activity at the time of observation , yielding the first published color measurements of the bare nuclei of 167P and P/2008 CL94 without possible coma contamination .
Activity was detected on P/2011 S1 and C/2012 Q1 , yielding relatively high estimated mass loss rates of 140 \pm 20 and 250 \pm 40 kg/s , respectively .
The colors of the dormant nuclei are consistent with the previously-published colors , indicating that any effect of non-geometric scattering from Centaur dust or blanketing debris on the measured colors is minimal .
The results of our observations are discussed in the context of the cause of Centaur activity and the color distributions of active and inactive Centaurs .
We suggest that the relative paucity of red Centaurs with low-perihelion orbits may not be directly due to the blanketing of the surface by unweathered particulates , but could instead be a result of the higher levels of thermal processing on low-perihelion Centaurs in general .