I recently ran a course in the Welsh lake district - the Elan Valley reservoirs, where there are many marvellous subjects to paint, including glorious river scenery. With this rather cold spring weather it was important to find locations where students could work out of doors in reasonable comfort, and as there are many sheltered spots in the Elan Valley area we were able to work quite happily.
Although it was mid-summer, I haven't used many greens in the painting, much of the foliage achieved with a deliberately dull blue-grey, created by mixing French ultramarine and yellow ochre, a rather opaque colour. This dullness helps to accentuate the bright yellow tree. With foliage, edges get lost easily, as they run into one another, and you can see how I've introduced light edges of foliage by painting the darker washes around the edge. It pays to look at the scene through half-closed eyes as this will eliminate much detail and allow you to pick out the more important aspects of the scene, both in terms of tone and detail. Please don't try jumping into rivers to get your paintings done - not only can it be costly in lost equipment, but it can also be rather dangerous in the wrong place!