  A study of the particle multiplicity between jets with large rapidity
separation has been performed using the D{\O}detector at the Fermilab Tevatron
$p\bar{p}$ Collider operating at $\sqrt{s}=1.8$ TeV. A significant excess of
low-multiplicity events is observed above the expectation for color-exchange
processes. The measured fractional excess is $1.07 \pm 0.10({\rm stat})^{+
0.25}_{- 0.13}({\rm syst})%$, which is consistent with a strongly-interacting
color-singlet (colorless) exchange process and cannot be explained by
electroweak exchange alone. A lower limit of 0.80% (95% C.L.) is obtained on
the fraction of dijet events with color-singlet exchange, independent of the
rapidity gap survival probability.
