Hi Cavesson. It looks great so far but you need a couple of things.
•Denser shading. The coloring looks great but you need dark shading in order to help it fit in its background. You can use a black airbrush with a light opacity and add the shading. What helps is you can see the shading already and just need to make it darker.
•Color balance hue. You have a green background with dense woods which means you need to add a light hue to the horse in order for it to fit in better. Usually, all art programs have a color balance scale where you can add different colors. You probably need to add a small percentage of green with a small percentage of yellow as well.
•You still need the mane and tail, the two hooves, and the drop shadow of the horse, but I assume you already know that. LOL.
Other than that it looks great!