Jan..... RL makes a DeepTone Primer for these colors. If you use the primer - this product covers very well in two coats. I have used it many times - it works very well.
I don't know if the store that sold you the product recommended the Deeptone? If they didn't - shame on them. If you didn't think you needed it - shame on you.
Your error was in not using the primer. ANY - and I do mean ANY paint manufacturer that makes dark colors will have this problem - Benjamin Moore - Sherwin Williams - even Anchor (who I have not heard of).
In order to make colors like this - the paint doesn't have any pigment in it - just colorant. Imagine a glass of water - add red food coloring - what do you have? Red water - but it is still water - transparent. Dark color paint is the same way. Any company's dark color paint is this way - it is simple paint chemistry.
Please don't blame the RL paint - it would have happened with any product.
Next time ask about a deeptone primer when you use a dark color - it makes all the difference in the world.