You're really doing great so far! How many colors in your set do you have? Layering is going to be a great skill to learn, even if it's just 2 layers. When you look at a horse, look at it with a colored eye & look for colors... In bays you'll see some yellow hues, browns, a little bit of black, and maybe red/orange (always keep in mind lighting). When you build up your colors, you're going to create a more lifelike feel to your drawings .
I lay my darks on first, and then overlay them with the other colors. Others start light, work to dark... it depends on what you find works for you! I found this fantastic 2-part tutorial that might help?