All you want to know about painting: "routine" colour choices

The next question in "All you want to know about painting" series comes from +Terrill Welch: 

What has an artist limit their colour palette in such a way that all their work looks like it is painted on the same day at the same time of day? Or with no light reference at all? This might be asked more accurately as what is the influence of artificial lighting and colour theory in painting? Or maybe it has to do with this idea of creating a solid body of work in one style? I have no idea. I am just puzzled when I notice this result in an artist's work - my own included at times. I wonder - what is really happening here? 

Pablo Picasso. Old blind man with boy. 125x92 cm. Oil/canvas. 1903

It seems to me that there are many questions in one here, and I would like to split the topic. First of all, I'll save the influence of artificial lighting and colour theory on painting for later; also (and this is a partly related issue), I will, for now, exclude the cases where a painter limits their colour palette deliberately, with a conscious expressive intent. In such cases, I believe, it's more or less clear what's happening (even if it's not always easy to express in words). 
Here is one of the most famous examples of this, from Picasso's "blue period", as an illustration of what I mean. 

It seems to me you are asking rather about situations where an artist "falls" into a limited range of colour harmonies without conscious intent, almost without noticing it. Obviously, we can never know for sure about other painters, but you mention your own work -- and more generally, I know that such things do often happen unintentionally, as a result of choices made unconsciously. No wonder, since, apparently, all our actions are initiated unconsciously...  

I believe there is a very general reason for this kind of unintentional repetitiveness: in most general terms, the more frequently one does something, the more likely they are to do the exact same thing in the future, especially if one somehow gets a positive feedback from earlier times. That's just how the neural underpinnings of our inner lives work: the more we do something, the "stronger" the neural pathways for doing it; and the stronger the neural pathway, the more likely it is to get activated again, and again, and again. This is essentially the same mechanism one can use deliberately to develop a certain habit (and I believe it's also related to what people sometimes call "comfort zone"). 

So, if a painter has successfully used a certain colour harmony -- and falling in love with the resulting painting created a positive feedback for their unconscious, they are likely to take the same path again. And the more they do it, the more likely they are to repeat it. And then it just might happen that you look back at your own work and suddenly see the repetitiveness you haven't noticed in the process, the limitations you unconsciously imposed upon yourself, as though you've become addicted to a certain colour harmony. 

It may happen with colour harmony, or it may happen with some other aspect of your work -- the mechanism is the same. As far as I know, the only way out (if you don't like it) is to make a conscious effort to "shake off" this unwanted routine. One can use some totally different subject matter to paint, or one can actually limit the palette in a novel way, to force oneself to work with other colour harmonies. I know some painters deliberately eliminate some favourite and seemingly essential pigments from their palette when they feel themselves falling into routine, automatic colour choices. 

But one way or another, the most important thing is to be aware of the effect, and to make a conscious effort to counteract this tendency. And the good thing: this, too, becomes easier with repetition -- the same mechanism "wired" into our brains is now consciously exploited for another goal!