Watercolour and oil painting are two techniques requiring two different strategies. Watercolour is a transparent pigment while oil is opaque (unless one paints oils using thin layers of washed pigment, which is not my case). My flimsy brain needs to adapt to the two methods when I go from one technique to the other. For watercolour, the light colours are painted first and the darker colours are implemented afterwards.
In oils I always start with the darker colours and make my way to the lighter ones. The two methods are very different and give different results. Watercolour will tint the paper while oils will stay on the surface of the canvas. I often add pencil strokes, charcoal or ink to my watercolours in order to give them more power.