MixRGB nodes don't add up Value as I expected. What knowledge am I missing? Why don't these add up to 1?

I have seven RGB Input Nodes that are greyscale and have Value of the following amounts:

0.18333
0.2
0.15
0.18333
0.1
0.06667
0.11667


I would expect these to add up to 1 and become white, but that is not what happens. 

Instead I get a dull grey (#686868):  Why is this?
(There are no other lights in the scene.)

This is my node set-up:



Next I tried using Add Shaders to see if that would make a difference, but it did not:





Update &amp; semi-answer: This works ↓ (but I don't know why)

I had been adding the Value:



I should be adding the RGB if I want them to add up to white: 



I didn't realize that the value is sort of a result of the RGB. Nodes that add are adding the RGB, not the Value.

(I'd be happy to accept an answer that explains how the two are related.)
The answer is probably in here somewhere.
Go get white you have to pass something that will increase the color. For example... You have add and a factor of 1.000. This means you are not mixing the colors, but instead using one input of the node.

Just curious though, what are you trying to do? Why not just use a white shader?