Unfortunately, this is common to several colors in the LEGO color pallette. According to this article on Eurobricks.com, The LEGO Group (TLG) made a change in the early 2000’s in how they make their colors: they used to have premixed color granules but abandoned those in favor of a system of white granules with colored dyes added in. This new system allows ...
The color of the 2x4 plate and 1x2 jumpers in the photo appears to be regular Dark Blue:
The greenish tint you mention is likely discoloration. Here is an example of a discolored regular blue piece (right) next to a fairly new regular blue piece (left) for comparison:
How uniform or consistent the discoloraton is depends on the cause and/or ...
This is an excellent question. Here's my best guess as to why this is.
As you've pointed out, LEGO System Minifigures were made with yellow heads from the start for a specific reason. On Lego.com it states:
We chose yellow to avoid assigning a specific ethnicity in sets that don't include any specific characters. With this neutral color, fans can assign ...
You can look for missing data in currently available lists:
Old school Peeron (no longer updated)
Bricklink list most of the brick colors available for sale.
Rebrickable has attempted to bring all colors in one place.
Brickset has also some details.
Mecabricks has one also (as PDF).
LDraw project has such list.
It would also be good to define term "...
This color chart is from LEGO's Digital Draw program.
After doing a quick skim of it, I know you're missing the "Legacy" colors. Whatever "Legacy" means here, I don't know.
Colors read from Left to Right:
316 - Titanium Metallic
315 - Silver Metallic
309 - Metalized Silver
297 - Warm Gold
310 - Metalized Gold
298 - Cool Silver, ...