Humm... you are doing much better than when I first touch colour. I think the brightness/value should be your main concern here. Looking at the painting here, it's like the colours are likely "washed", or like very close in brightness. If you compare that leyendecker one, your green seems too light and the white seems too dark. The HSV colour picker is not a constant-brightness one, which means if you dial the hue, the brightness would change. You could probably use HSL/HSI' picker and you can see much more clearly why you need to keep your brightness in check. A way to keep yourself sensitive to the full value range is you could paint a pure white and pure black in adjacent somewhere on your screen so you could immediately see the range you are working on, so it's less likely to fall into the "ok I think this is dark/light enough" trap.