I am not sure you will be able to talk about "highlighting" of information, as it doesn't really define anything by itself. What is a highlighted element? Maybe something that needs to be made clear in comparison to other information. The argument could get too vague. How about you go for **readability** instead? In the first case, your argument should have to be "I didn't notice that part of information was important". In the second, "I didn't consider the message, because I never really noticed it". 

One of the main influences of readability is contrast. Arthur & Passini described in their book [**Wayfinding**][1] from 1992 a reliable method to calculate the contrast difference between two colors:

> The formula is based on the [light reflectancy (LR)][2] readings in
> percentages for each of the two colors involved. By substracting the
> darker color from the lighter color, divided by the difference by the
> lighter, and multiplying by 100, we get **brightness differential**. When
> the brightness differential is 70 percent or higher the legibility is
> assured. When it is less, the legibility cannot be assured and those
> colors should not be using in that combination.

I don't know how grey your grey was, but if you could get a low differential that could certainly help. It would probably also be relevant that the reference is about architecture, graphics and verbal human interaction. 

![enter image description here][3]

![enter image description here][4]

([Source][5])


  [1]: http://books.google.co.nz/books/about/Wayfinding.html?id=lmpQAAAAMAAJ&redir_esc=y
  [2]: https://en.wikipedia.org/wiki/Light_Reflectance_Value
  [3]: https://i.sstatic.net/RVxJM.png
  [4]: https://i.sstatic.net/NfHr3.png
  [5]: http://www.writer2001.com/colwebcontrast.htm