Let R be a ring and Z(R) be the set of zero divisors of R. The regular graph of R, denoted by Γ(R) is the graph with vertex set R\Z(R) and {X, Y } is an edge if X +Y ∈ Z(R). We prove that the chromatic number of Γ(M n (F q )) is at least (q/4) n/2 , where M n (F q ) is the ring of n × n matrices over F q , q being an odd prime power. This proves that the chromatic number of Γ(M n (F alg p )) is infinite, answering a case of a question posed in BCC22.