Painting plastic deck as wood. Again.

Greetings. I've read all the topics I could find on painting plastic deck as wood, and the usual advice is to paint it black, then paing it light color like tan or concrete, and then scrub the plastic grain with knife or sand paper. Okay, I've tried that, and here is what I've got:

I've airbrushed first layer Vallejo black, then added a layer of pollyscale gloss, for protection, than airbrushed some other colors to check which one will be the best. Today I've tried to scrub it, and the black paint went off together with upper layer, so that bare plastic is seen as wooden grain. No matter how light I'm trying to scrub it.

I've gave a 24 hours to cure for each color. 

What am I doing wrong, and how to do it right? :)

On the other side of the deck I've tried a number of oil washes. 

That went a bit better, but it's a bit too intensive color for a deck of Le Glorieux. :)

What advice can anyone give me on how to improve the grain? Which colors do you prefer as main for a deck - grey, tan, beige, yellowish, light wood? And so on. If possible, post closeups of your decks, with descriptions on painting techniques. Thank you.