Okay right off the bat, split this into four separate pieces. The length of this post isn't helping anything and even if these four illustrations were sequential and told a story the format is too long to read in any clear way. Presentation of your art is almost as important as the actual art itself, so always try present art in a way that benefits the pieces themselves.
For starters you need to work on anatomy; the clarity of the action of your characters is held back in some instances by anatomical issues that sort of muddy what is happening (particularly in the first scene and the bottom scene). I like that you're putting these characters in very dynamic poses and situations, your ambition is good, and over time you will pick up better anatomy if you keep at it; so don't worry too much about that aspect of it. But definitely keep in mind that you should be working at it.
Your use of line of action isn't quite there either, this is part of anatomy and knowing what poses suit the character and the action of the character. This is most noticeable in the red girl with the scythe swinging it. Her pose and the motion on the scythe are not flowing together, creating something of a disconnect. Same with the orange dude in the bottom. There should be a single line of action that flows consistently through the pose of the character into the weapon they're swinging. Only being disrupted if they're being hit or at the point of impact on their target. Look up videos and stills of martial artists and dancers, if you do enough research you can find a lot of action poses to use as references for combat poses. Working from reference is absolutely vital to learning anatomy.
As I mentioned earlier, you're tackling a lot in all of these scenes, which is fine, but I recommend you get a sketchbook and do a lot of more focused studies. Work on anatomy, and also ways to communicate depth. It's not a lot of fun to do, but set up some basic blocks and draw what you see and work on rendering. If want to draw scenes with lots of action and multiple characters you need to learn to communicate distance in a 3D space and how distort it as well.
As for color, my first instinct would be to say ignore that for now and work on more fundamental aspects of art before getting into color.
I will say though, that your color choice isn't bad by any means, but your implementation of the color is a bit too much. You're hitting very high saturation for every part of every scene. It's better to have areas that are less saturated to create more visual interest in the parts that are saturated, it also helps guide the eye through the action by acting like a highlighter. If everything is highlighted how does the eye know where to go?
Your value scale is actually pretty good overall. When I convert this to black and white the scenes become much more legible and less busy. There are some areas where a little more or a little less contrast would be ideal, but it's solid.
The last point I want to make is on the intent of your brush strokes. This is a little difficult to explain; but on elements like the energy beams and blasts and fog effects, I want you to consider how intentional are you being when making them? As they are, the brush you're using to make them looks to be doing the most when informing their shape, form and look. This creates a weird sort of collage effect, that I don't think you're looking for in your work. So you have these characters that you've drawn yourself mixed in with these effects that are partially you, but mostly the program. My advice is to do everything in your drawing with linework. If you want smoke, draw the lines to make smoke clouds. If you want lasers, draw in the lasers yourself. This will give your work better cohesion overall.
A few things you should also look into:
The Gestalt Principles
Hope that helps, any questions or clarifications, pm me.