Back when I lived in So.Cal. one of our favorite night spots was a Mexican restaurant & bar in Hollywood named Carlos & Charlie's. They had great food (although quite non-traditional) and Margaritas. One of my favorites were their enchiladas. These had a darker sauce then the traditional brick red traditional enchilada sauce, that was seriously laced with olive (with sliced black olives in adornment).
I have tried recreating this over the years with varying degrees of success... using olive oil in place of more unflavored oil, and puréed olives in addition to the more traditional enchilada sauce ingredients, but I have never hit this nail squarely on the head. Not sure if this is another traditional thing I was just never aware of, or they just hit it out of the park on their own.
So I thought I'd throw it out here to see if any of you prepare something akin to the above. I Googl'd it and found several copycat recipes for their tasty tuna dip, alas nothing about their enchiladas (sauce).
I have enclosed a color swatch which is my pretty firm recollection of the sauce's color.