detection potentially indicating a collapsed core [@Tanaka2010]. The comparably high galaxy overdensity surrounding C (Figure \[fig:density\]) suggests that this RLAGN is surrounded by a protocluster consisting of a dominant main halo that is already a relatively high-mass group.

The approximate mass of 7C can be estimated from the galaxy richness. @Andreon2014b reported that galaxy richness was a good proxy for cluster mass, with little dependence on redshift. ClG0218.3$-$0530 has an X-ray determined mass of 4-8$\times10^{13}$ [@Tanaka2010; @Pierre2012], which is consistent with the galaxy velocity dispersion [@Tran2015]. Since 7C is richer than ClG0218.3$-$0530, its mass is likely to be slightly greater. Using equation 3 from @Andreon2014b, and the calculated value of $m^*_{4.5\mu m}+1 = 21.2$ from @Wylezalek2014 we measure a cluster richness of $10\pm1$ galaxies[^5] with $[4.5]\le21.2$, and estimate the mass within 500kpc of C to be $(9.2\pm4.5)\times10^{13}$M$_{\odot}$, consistent with this structure being a slightly more massive group than ClG0218.3$-$0530.

Red sequence and red fraction {#sec:CMD}
-----------------------------

One of the signs of a mature cluster is the presence of a red sequence. Ubiquitous in clusters at $z<1$, red sequences persist in galaxy clusters out to at least $z=1.4$ [@Stanford2005; @Snyder2012], and have been found in some dense (proto)clusters at even higher 