SUND[a, b, c] are the symmetric SU(N) d_{abc}.
Overview, SUNDelta, SUNF, SUNSimplify.
SUND[a, b, c]d^{abc}
SUND[a, b, c, Explicit -> True]2 \left(\text{tr}(T^a.T^b.T^c)\right)+2 \left(\text{tr}(T^b.T^a.T^c)\right)
SUND[c, a, b]d^{abc}
SUND[a, b, b]d^{abb}
SUNSimplify[SUND[a, b, c] SUND[a, b, c]]-2 \left(4-C_A^2\right) C_F
SUNSimplify[SUND[a, b, c] SUND[a, b, c], SUNNToCACF -> False] // Factor2\frac{\left(1-N^2\right) \left(4-N^2\right)}{N}
SUNSimplify[SUND[a, b, c] SUND[e, b, c], SUNNToCACF -> False] // Factor2-\frac{\left(4-N^2\right) \delta ^{ae}}{N}
SUND[a, b, c] // StandardForm
(*SUND[a, b, c]*)SUND[a, b, c] // FCI // StandardForm
(*SUND[SUNIndex[a], SUNIndex[b], SUNIndex[c]]*)SUND[a, b, c] // FCI // FCE // StandardForm
(*SUND[a, b, c]*)