The tricolor (tri) pattern in the tri XL American Bully is primarily influenced by the Agouti gene, specifically the 'at' allele at the Agouti gene locus. This allele is responsible for the tan point pattern that includes markings typically found above the eyes, on the cheeks, chest, and legs of the dog. For an XL Bully to exhibit this tricolor pattern, it must inherit at least one 'at' allele from each parent. Additionally, the expression of these tan points can be affected by other genes, such as the K Locus for black pigmentation, which can influence the intensity and distribution of the black and tan colors in the coat.