  We present the detailed computation of full-color three-loop three-point form
factors of both the stress-tensor supermultiplet and a length-three BPS
operator in N=4 SYM. The integrands are constructed based on the
color-kinematics (CK) duality and generalized unitarity method. An interesting
observation is that the CK-dual integrands contain a large number of free
parameters. We discuss the origin of these free parameters in detail and check
that they cancel in the simplified integrands. We further perform the numerical
evaluation of the integrals at a special kinematics point using public packages
FIESTA and pySecDec based on the sector-decomposition approach. We find that
the numerical computation can be significantly simplified by expressing the
integrals in terms of uniformly transcendental basis, although the final
three-loop computations still require large computational resources. Having the
full-color numerical results, we verify that the non-planar infrared
divergences reproduce the non-dipole structures, which firstly appear at three
loops. As for the finite remainder functions, we check that the numerical
planar remainder for the stress-tensor supermultiplet is consistent with the
known result of the bootstrap computation. We also obtain for the first time
the numerical results of the three-loop non-planar remainder for the
stress-tensor supermultiplet as well as the three-loop remainder for the
length-three operator.
