There's a lesson I like to teach in which I show my students how to find the value (or tone) of a color by underpainting in complements. If you force yourself to carefully choose the closest opposite color in the closest possible value match to what's there, you can't help but learn a lot about color and value. This is my photo:
I use a color print and a grayscale version of it.
I start with Wallis paper, toned a pale neutral color, and draw the values in charcoal, as well as using a white plastic eraser to establish the whites:
I then use the color photo and carefully select the correct value in a complementary color. Here you can see that the pale blue sky is a pale orange sky:
I fill in one layer of all the correct values in complementary colors:
Then I use the grayscale print, so I don't get confused looking at the 'real' colors, and continue painting with the complementary colors, which results in this:

And for my final painting, I go back over the entire thing with the colors of nature, the 'real' colors, to create a lovely tonal painting with wonderful, rich color:

Mesa Meadow
pastel on 17x11" Wallis sandpaper
$500 delivered to you ready to frame