Chromatic polynomial and the $\mathfrak{so}$ weight system

In a recent paper by M.Kazarian and the second author, a recurrence for the Lie algebras $\mathfrak{so}(N)$ weight systems has been suggested; the recurrence allows one to construct the universal $\mathfrak{so}$ weight system. The construction is based on an extension of the $\mathfrak{so}$ weight systems to permutations. Another recent paper, by M. Kazarian, N. Kodaneva, and the first author, shows that under the substitution $C_m=xN^{m-1}, m=1,2,\dots,$ for the Casimir elements $C_m$, the leading term in $N$ of the value of the universal $\mathfrak{gl}$ weight system becomes the chromatic polynomial of the intersection graph of the chord diagram. In the present paper, we establish a similar result for the universal $\mathfrak{so}$ weight system. That is, we show that the leading term of the universal $\mathfrak{so}$ weight system also becomes the chromatic polynomial under a specific substitution.