So...the most important seeing skill for painting from life is looking at things in relation to other things and not looking at them one at a time. Yes, you can only paint things one at a time but you CAN see them in relation beforehand. Human vision is like a camera at f2. The object in focus is crisp and well lit but everything else isn't. UNTIL you look at somewhere else...in which case your eye immediately adjusts for that distance and that level of illumination and the new thing snaps into focus.
If you stare down one item at a time when you paint, everything has a hard edge, there's no atmospheric perspective, values are off, colors - especially greens - all become too similar. The list goes on...and the painting looks flat and amateurish.
Here's an example where the foliage and its illumination in various areas was quite similar, since the species of tree along this river isn't widely varied. I picked colors by keeping one area as my focus and judging the colors of the other areas by what I saw in my peripheral vision.
The close tree is a richer, darker green. The far trees are lighter, more gray and have less textural detail.
Perhaps you can see how similar the greens here were from the location shot below (I understand it will get larger if you tap it? My tech mentor, artist Jessica Kirby, is working hard to flatten my learning curve. I also need her to show me how to put her blog on the side, below).
Yeah, I left out the bridge...but had I put it, in the trees behind it would have been reduced to a slab of untextured grey-green. Just what my peripheral vision would see with the closer items in focus.