As you mentioned, a LOT of people are unhappy with Ralph Lauren Paints. (If you search this site and other Forums for 'ralph lauren', you'll see.) Anyway, it's not unusual for dark colored paints to require multiple coats. It's always best to prime whatever your painting with a GOOD primer before you paint to insure an 'even/sealed' under-surface. In short, by not priming, different parts of the surface of whatever your painting may absorbe your paint at different rates, hence, showing light and dark areas. (You see, some paints act as a sealer too and, thus, require a 2nd coat to even things out.) Even if the surface your painting is white you want to prime. Why still??? Because dark paint may require multiple applications anyway. (I'm not implying you didn't prime; it's more of an FYI as to why one should prime ...)
It's one thing if a manufacturer touts its product to give 'one coat coverage' over 400 sq. ft. and NOT do so. I suggest 3 things if you're up for it. Did the retailer help you with this problem? (So-to-speak false advertising.) Write to your state's Attorney General just as you did here, also including where you bought your paint, what you did in regards to the 'Painting Preparation Instructions' on the can, a copy of the receipt, a copy of the info on the can (as you stated), and what happened when you tried for a remedy. AND, write to the state Attorney General in the state that MADE the paint with the same aforementioned info. Personally, I'd do it. At least you'd vent in another productive way. Of course, you're in your right to let 'everyone' know of your experiences with all this.
I know it's not much consolation for you to hear. You can get custom paint mixtures made too. Bring a sample, (wet & dry), with you to any retail paint store that will mix custom colors. I suggest you stay out of the Home Centers (even though my 3 year old daughter is a Home Depot stockholder) because their paints may be of a lesser quality than the specialy paint stores. Finneran & Haley, MAB, Sherwin Williams, etc., etc., are the types of stores I'd send you too. If they don't do custom paints, then you're relegated to the Home Centers. (No matter.) You'll pay good $$$ but it's worth it. BUT, you have shown that good $$$ doesn't necessarily guarantee you good paint. (Let the retailers you visit know what happened. Bring the can with you too.) I don't use any paint that's not off the shelf (personal preference), and in all cases, I've had great personal luck with Finneran & Haley. I spend about $26/gal. for their Low Luster. (You can find all the paint retailers in your area in the Yellow Pages under 'Paint'. My best to ya and hope you do better.