I think it means his moods and world-focus were erratic. One moment he was in a random fury about gigantic important things in the real world, the next moment doing something patient on something outwardly really unimportant as if the world outside didn't exist. Noting the earlier question about adjusting a red to a blue, it could here mean changing (a patch of) one colour into/toward another.
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red appleI mean is he talking about his decision to change his style in the future or is he talking about that he has changed his style?The history of the changes in his style is not included in the quote, so Guston himself is not saying anything about those things. Here's what Guston said and what it means: