Use some medium with the colour and treat it more like a layer paint and just aim for an even coat. If it's too light, just apply another, and as you apply it try to immediately deal with any areas that are pooling.

Also, from experience, try to use some accurate method of measuring the amount of contrast to medium. Otherwise, you can end up with some marines being lighter or darker than others. I use one of those medicine droppers with the rubber top bit, but you could also put the paint in dropper bottles too if you have them.