Experimenting with Color

I have been told about the additive color turning to white since my high school painting class, and again in my 2-D design class, and again in my 3-D design class, but none of my instructors have ever brought in light and said, "this is how it works." Although the information has been put in front of me before, it was nice to see the actual process first hand. As for the subtractive color experiment, I have seen that happen every time I clean a paintbrush in a bucket of water. I have never made black from the primaries before though, and as aggravating a process as it is in small amounts of color, when I put it together in a jar, it was easy. I like the way it shades the colors more than using that Mars black out of the tube. I know they are supposed to technically be the same thing, but it seems like the combination black in the jar I have now makes a nicer color for shading... except my yellow keeps turning green. But not just a "yucky yellow" green, more like an "oops my black is too blue" green. I guess I am asking if that's ok?