  We obtain the full-color four-loop three-point form factor of the
stress-tensor supermultiplet in N=4 SYM, based on the color-kinematics (CK)
duality and generalized unitarity method. The CK-dual solution, while
manifesting all dual Jacobi relations and satisfying the minimal power-counting
of loop momenta, lies in a 133-dimensional solution space. We also show that
the planar form factor integrand satisfies precisely a directional dual
conformal symmetry in the lightlike limit of the operator momentum, which is
supported by explicit four-loop calculations.
