Painting plein air ... the French term for painting in the open air ... is the best way to learn about proportions, weight, perspective, and best of all, to see all the "real" colors in nature! And, you usually remember how the weather was ... hot, cold, wet, dry, etc.
For this painting, an 11x14" pastel, I was in the Red Rocks area near Las Vegas for the 1st Plein Air Convention and it was our first day out of the convention center sessions to paint. It was cold, and rain started coming in about half way through my painting. If you look closely, you can see where some of the light rain drops hit the surface. It added to the painting, so I was not about to change it.
Special? ... can be the artist's story about the painting. If you attend a gallery opening or show, admire a painting, and get to meet the artist, ask them about the story behind the painting. Meeting the artist and hearing the story, may be what you need to make a decision to purchase that painting. Get to know an artist ... you might have some fun hearing a story!