Really cool stuff man!
Before we go any further let's just talk about a few things.
You are going with a style that is very minimalistic. This means you need to make things iconic. For example, your faces are a blank colour with a big, bright red nose on it. That's all you're using to define that this is a human's face (and some hair). You'll need to use this kind of iconography throughout your game for consistency and because you have such a limited amount of space to work with.
You also won't have space for outlines and other things we sometimes use to highlight certain points of focus, for this reason you're going to have to rely heavily on your contrast and saturation to show the player what he/she should be focusing on.
Here's an edit to show a few of these things next to yours for comparison:

Iconography - I made the hearts one solid colour and added saturation to them. Your life is important in games like this and the player needs to be able to see them quickly and clearly.
Saturation - Your HUD outlines don't need to stand out, just be there, so less saturation. Your backgrounds must not distract from the characters/spells/weapons/enemies going on, so we desaturate it. You'll notice this makes your character really pop off the screen. I added more saturation to some of the parts of your character as well to really make his stand out.
Contrast - You haven't made your textures properly yet, but for when you do make sure there is low contrast on things that aren't actually important. Here I added a simple, small pattern to the back wall. You can tell they're bricks, and there is some variation, but no one is going to become confused or distracted by it. Same with the small rocks on the floor. All low contrast, few colours so that the player doesn't see it. Hue changes work best for defining things when you have very little contrast/saturation to work with; which is why those stones are noticeable (compared to the bricks in the wall), but still don't distract.
I also removed pure greys from your palette - no one likes pure greys. Just make them slightly blue or yellow or something; it's just more interesting to the eye like that.
All these changes are made for readability and will greatly improve your final experience playing the game (and will help you make sure the player is always aware of what you want them to be aware of.
This is of course all assuming it's a game where you need to be able to discern things quickly.
EDIT:
Before you think this is the only way to do things (I realise I didn't actually say this, but the changes I made are simply a suggestion of how you
could achieve clarity), I actually just spied
a new piece of pixel art from PixelJoint that uses minimalistic style, but has lots of saturation and still has easily distinguishable characters.