I have a feeling that won't cease I think in any time soon. And that is that I stink (artistically :-) ). My visions in my head are always better that outcome on the canvas. I think we all feel that and it is natural. Nevertheless it is important even in times of great disgust with ourself to push through and persevere. One of the action for that is to do some basic exercise from time to time.
It's a great advise from any great instructional book on art that you should learn to see colours in the temperature relationship and warm and cool painting with just two colours is a great opportunity how to see this relationships.
I started my exercise with ultramarine blue and raw Sienna according to my favourite book (thanks to Juliette Aristides: https://books.google.cz/books/about/Lessons_in_Classical_Painting.html?id=SCuJDAAAQBAJ&redir_esc=y
I did a mixtures between the two colours and lighten them in ten steps with white and made this colour chart:
That provided me with an information of which range is achievable with those colours.
Next step was to set up a still life that would be manageable with this range of colours. So I put into my shadow box a pumpkin (warm orange) and blue plate with some blue cloth underneath.
On the image you can see my setup. It was a quick study approximately 4x6 inches just in sake of a practise. You can see my chart above the painting to guide me.
Here's the outcome. As you can see you're able to achieve a lot just with two colours (plus white). Some things has to be downplayed greatly - for example the green stalk of the pumpkin - but you can achieve believability by mixing a colour that is not green at all but have relative temperature right to adjacent colours! And that's the key of this exercise)
I was so focused on the colours that I put to much of a detail in cloth and the background which ruined the picture but in overall I think the exercise served the purpose.
I would like to know in comments your suggestions how else to train warm - cool relationships. I strive to get better in this so any advise would be appreciated greatly.