Most of the world is made up of neutrals, at least Ireland is, and Seattle, for that matter. All the "emerald green" is real enough, for sure, but even that has a little bit of red in the mix to keep it earthbound. Here are a few images that rely for their beauty on subtle color dominance amid greys and browns.
Pick one of these you'd like to paint. Starting with a palette limited to one red, one yellow and one blue, spend some time just mixing patches of the complex colors you see.
When you're ready to begin a painting, keep the compositions simple, paying close attention to getting the values in the ballpark. For each shape, ask what in the image is darker and what is lighter. For example, in the picture immediately below, the crest of the hill should be darker than the clouds, but lighter than the brambles.
Similarly, ask what is warmer and what is cooler. In the bottom picture, for example, the water is cooler than the sand, but warmer than the sky. A little.
Have fun. It's not necessary to get your painting exactly "right"The range of what works is most likely wider than you think. The real purpose of this exercise is to practice mixing subtle neutrals, and to appreciate the role they play in a great many scenes.