Color mixing results

I mixed the Phthalo Blue and Dioxazine purple, as discussed in my last post:

 

I could tell right away that the shade would dry too dark, but I tried it anyway:

This was how dark it was wet, and I knew it would dry even darker. I wiped it up with naptha and a paper towel. I added a drop of Titanium White, and at first I was afraid I made it too light:

Actually, it still dried too dark. I added another half-drop of white, and then it was pretty much spot on. Here are a few sections that I touched up:

So is mixing based on the Magic Palette chart the only answer? Fortunately, no. I also bought this handy color matching guide, which showed that Cobalt Blue should be a great spot match:

I decided to try Cobalt Blue straight out of the tube, and it was almost identical to my mixture of purple, blue and white!

In summary, what have I learned?

• The Color Mixing Guide is great for matching hue, but I had to add white to get the right shade
• The Color Matching Guide more accurately matches the shades of artist colors out of the tube (for Liquitex "Basics", anyway).
• Don't bother with the Color Mixing Guide if you find a match with the Color Matching Guide.
• It only took a tiny amount of paint to touch up the entire playfield; a little goes a long way.

Note that the Color Matching Guide only has 36 colors (180 tints/shades), while the Color Mixing Guide has 841 (29 * 29 colors). I'd guess that most playfields originally used a small palette of artist colors, but these may have yellowed with age. This makes it necessary to tint the original color to match. Maybe Liquitex should sell a "cigarette smoke stain" hue. 

I'm hoping that someone can explain something. Why do these 2 color guides, from the same company, have two different shades/tints for the same color?