For the white ones at least... white clouds usually have even a hint of grey or yellow in them. Actually, that can apply to all clouds, no matter how technicolor they are.
Try to avoid duotone clouds. Add some grey. Add some blue. Add some yellow. Add some brown. Ad some BRIGHT white. Blinding white. Remember, more yellow in highlights, more blue in shadows. No matter what. (or at least, in sunlight. Try purples and pinks and blues for sunset. Greys and greyblues for storm clouds. Take or find lots of pictures of clouds, and then go in the color picker.
There will be yellows in the highlights, and blues in the shadows. Go crazy with the color picker. Dont need to USE those colors, but just loo at how the colors slide all over the color spectrum. Go outside and stare at the clouds. What shapes do they form? What hints of color are there?
Your skills in making the clouds are also needing some work. There are MANY different types of clouds. Whispy ones. Huge bulbous ones. Skidmarks. Depends on the wind.or atmosphere
Go to a weather site. Look up different cloud types.
One star for originality, as these are basically all the same clouds, but with different colors, and angles
Your first one is your strongest, color wise. I can pick out three different colors at least, and that is why I keep looking back at it