The fact that the male is chasing the female doesn't mean to much, they are usually aggressive to females. The fact that they have turned a dark blue is another story. This CAN be an indicator, it's not a sure thing, but they usually don't get to have very dark coloration if they are just happy in their tank. If the female is getting plump, this means she has eggs (obviously) and is coming into breeding condidtion. The male, can, get very amazing color when he is in breeding condition, such as yellows and blues and purples on his pelvic fin. He will also develop a high dorsal fin. The fact that they both seem to be ready to breed, and the male hasn't built a bubble nest, shows me that the male might not be mature enough. If this is the case, it could take up to a few months to come into breeding condition. But chances are, because he is changing color and all, says to me that he isn't too far off.It could also be that he is just not willing to breed right now bcause they only breed about 3 times a year. The way you can help him out is by feeding them live foods, (frozen if you can't get live, but live is best) They also like some vegitables, like lettuce. One last thing is that they like water tempature at about 78-80 degrees. Hope this helps, any other questions, I'd be happy to try and get you the answers.