You have the right idea with choosing unique colors here and thinking outside the box, so kudos for that creativity. Just some pointers for technique that I hope you find helpful. When layering anything, be very gradual. Take your time. It looks like you may have just put 1-2 tones down in the crevices of the muscle. It is because of this immediacy of color change that things look rather unclean and , frankly, unreal. I think you have the idea, you just aren't executing it.
So think of it like this. Whether shading or highlighting, everything is a shape within a shape. In this case, it is the shape that the crevices between the muscles form. First, put down your mid tone. You do this just fine. It looks smooth and even. Now, take that mid tone and add just a tiny amount of that green. This will be the biggest shape in the crevices. Every additional shade you have will be darker AND fit inside of this shape. So run your first shade, which again is your mid skin tone with just a touch of green, and run it through the crevices. You don't even have to be all that careful, because the difference between this shade and your mid tone is very small, and so unless looked at very closely, it should be kind of tough to tell the difference. You're not only getting in the cracks here, but also the sides of the downward sloping muscles-that is the parts of the muscle leading into the cracks. Make sure you add a couple layers of this same shade. Now, go darker by just a little bit, and paint INSIDE of the boundary of your last shade. Again, the change in darkness is gradual enough that it blends on it's own almost. Next shade, do a little darker and smaller. Keep doing this until you are basically doing a thin thin line of your darkest green right at the lowest point of the cracks. TA DA! You have a blended gradient of shadow. Congratulations!!! Remember to let the paint dry between layers and to add enough coats per level of shade.
slow is smooth and smooth is fast. Take your time. You are running through minis too fast, and to be frank with you it presents a sloppy appearance in some cases. This is all fine and good if you are planning on painting a 5000 point Warhammer Army. But you're not, damnit. You're a display painter, and we value perfection, cleanliness, and creativity. For us, this is Art, not a game. In my above description, remember that first layer I told you about? The one where it is basically your mid tone with just a touch if green added? Well, in your WIP, that layer looks like a shade3 or shade4. Shade 3 and shade 4 should be small, deep in the cracks.
As Ten Ball says, apply a glaze of the mid tone and it should calm it down a bit. This should fix things, but once this dries, reapply some of that darker green in the depths of those muscle cracks.
Once you do this, repost and we will then talk about highlighting. You can do this, dammit, and I am going to be tough on you until I see the results you are capable of. Don't mean to get all drill sergeant on you, but I don't know another way. You know what to do, because we've all seen you make some big improvements. Let's kick it into high gear though and wow some people around here....
