Alias1

If they are Phenotype red, then they have two recessive red genes for the color. Black is dominant as is merle over solid. So say a Red Tri bred to a Red merle will produce only red tris and red merles unless that red merle was a double merle, then the litter would be prominently red merles.

Not hard but one just has too understand that red is recessive. Both parents must be or carry the gene. This is what is commonly called red factored.