  We rewrite the Zwanziger horizon condition in terms of the Kugo-Ojima
parameter for color confinement. This enables one to explain which value of the
Kugo-Ojima parameter is allowed if the horizon condition is imposed. Although
all the calculations are performed in the limit of vanishing Gribov parameter
for simplicity, the obtained value is consistent with the result of numerical
simulations. Consequently, the ghost propagator behaves like free and the gluon
propagator is non-vanishing at low momenta, in harmony with recent lattice
results and decoupling solution of the Schwinger-Dyson equation. The Kugo-Ojima
criterion is realized only when the restriction is removed.
