What is the difference with red, blue and yellow K-line boxes?

All of the boxes containing our 21" K-Line lightweight coaches are yellow/black. I think the Heavyweight boxes are black/silver.

The same box as the yellow top of the line, has shown up in bright red, blue and yellow lately online, I was wondering what, if any significance that had to scale?

The length is the same, so it has me confused, there is nothing online telling why the different colored red and black, blue and black and yellow and black boxes

As far as I can ascertain - The Blue and Yellow and the Red, White and Gold boxes are O-27.  

The Black & Silver, Black and Gold, and Yellow and Black COULD be scale. 
If they are Scale - it will say O Scale on the front of the box. 

From what I've seen, some boxes will also say "Semi-Scale"

There are also Blue and Black boxes (Same box design as Yellow and Black) which say O-27 on the box.

And Blue and Silver boxes for streamliners - O-27

Ok, the blue and black are marked o-27, so they must be the entry line, the red are marked o-27/0 scale, does this mean semi-scale?