Kathryn Law has been doing some paintings like this on her blog here, here and, here. We were swapping comments the other day, and I decided that I would give it a try. I told her I felt like I was about to jump into a lake where I knew the water would be really cold.
The colors I chose were Purple Lake, Magenta, Terre Verte, Chrome Yellow, and Cerulean Blue. I limited myself to five grabs, but one was an un marked tube that contained French Ultramarine Blue, which is a color I use all the time, so it was out. I also chose two tubes of Terra Verte, so I dropped one of those as well.
Gotta give myself some kind of chance you know.
The Terra Verte must have been from the days when I was still looking for the perfect tube of green. I tried em all. They all stink. Throw out your greens and just mix them. Terre Verte is stupid. It has no tinting power at all and I had to put tons of it into my mixes to change anything. Cerulean Blue is not far behind in tinting strength and it is not my favorite blue. My Purple lake was from so long ago that it was very dried up. I could not mix with it. Another one down. There went my darkest dark. Magenta is almost the same color though, not quite as dark and a little redder. It was going to be my "red". Chrome yellow was the lucky draw of all of them. I would have been sunk without it. The white was a given, so there I had my Grab Bag Palette. I was not that excited.

The grab, with piles of gray "mud" that were left over after some practice mixing.
I decided to see what they could do, you know, take them out for a test drive. I just mixed as many colors as I could come up with until my palette was full. Then, for fun, I layed them on a 6x8 board like my "Value Board" that I talked about in this post.
I had a ten step black and white value scale that I made with my workshop painters. The values were arranged along the edge of the board . I tried to line up the colors that I mixed using the new colors, by value, next to what I judged to be the value of each mix. This is actually a valuable exercise on seeing value. I also found that I was able to get a lot of good colors. That water was warming up.

In photoshop, I switched it to black and white to see how I did. There are some that are obviously off, but some were right on.
You may want to open another window and view the two enlargements side by side to compare. I am not an expert in photoshop or I would have put them together for you.

I finished the painting.
I'm working on getting a post together so I can share it with you all.