CF is one of the Casimir operator eigenvalues of SU(N) (CF = \frac{N^2-1}{2N}).
CF
Overview, CA, SUNSimplify.
C_F
SUNSimplify[CF, SUNNToCACF -> False]
\frac{N^2-1}{2 N}
SUNN
N
SUNSimplify[SUNN^2 - 1, SUNNToCACF -> True]
2 C_A C_F