Question: I was reading this [article](http://www.riagenic.com/archives/526) about Metro UI designs, and I was struck by this statement:

> 
> Example, if you look under the hood of a new car, you will see areas
>  colored yellow whereas the rest is the same color of the engine etc.
>  Car manufacturers do this on purpose, they want you to touch yellow
>  yourself but if it is not yellow and you are not mechanically minded –
>  leave alone.
> 
> 
> 

The author recommends using a color like Yellow as the **secondary color** as a means to draw people’s attention to the fact "I’m ok if you touch this, you won’t break anything if you do" thinking .I am a little unsure about this mentality that if you see something which is marked a different color other than the primary or background color,you would immediately mark it as a safe.

What are your views on it?

Answer: 
As the original author, i'll add my reasons:

It has to do with the fact pattern recognition is a built in component within humans, once we identify a familiar pattern it then becomes easier to seed.

The thing is, most users don't turn up to the average software as UX virgins? that is to say they aren't using a computer for the first time (some solutions are excluded of course). Typically the mainstream UX out there is often a horrible or confusing experience, all the primary / secondary color selection does is encourage that the user pick-up on the differences between chrome colors and input colors. Input colors = good!

It has a bit to do with extraneous cognitive load meets gestalt's laws of organisation.
That example illustrates some cognitive psychology, named here as grouping. Works splendid!

More examples of visual cues: 
<http://www.eruptingmind.com/depth-perception-cues-other-forms-of-perception/>

Perhaps you had something else in mind? If so, please elaborate your question.

Edit: Gestallt principles that is how it's called:
<http://www.interaction-design.org/encyclopedia/gestalt_principles_of_form_perception.html>