Take the highlights and shades further, the colours are too flat at the moment to really \"pop\". Try an exercise of painting a colour from black to white, try with red or blue, if you look at the RRM I did that with the sword, goes from black to white with midnight blue as the colour.
I wouldn\'t blackline, try this instead.
For bright minis undercoat white, then wash the areas with ink of appropriate colour*. Put it on really thick and maybe do a few coats. This gives you very dark recesses and starts off the highlighting stage by leaving the raised areas lighter. In a way its a kind of underpainting.
For dark minis undercoat black and just highlight up leaving a thin black edge, sometimes this might be too dark, if so, bascoat the area and then use a dark brown ink (or other dark ink of appropriate colour) to \"blackline\". Don\'t be afraid to use colours that are different to the main colour. One trick JRN uses is to glaze the whole model with a very dilute ink wash to give a tonal quality to the mini. I did something similar on my Druuchi anointed, the flesh was given some purple washes and tints to compliment the purple armour. This sort of thing needs to be done very subtly, remember you can always do another glaze, but you can\'t take the paint off.
* This depends entirely on the desired finish. I would use purple or purple+red or black + red for red (purple goes almost black, purple + red is lighter, red+black is browner), orange for yellow, green, green+brown or green+blue for green. The combos are something you will need to experiment with.