I have a Mma expression made with Print[...], e.g.:

[![output from Print statement][1]][1]


Now I want to give some explanations about some coefficients and for that purpose, I want to highlight e.g. coefficients a13 and a23 in light blue and a31 and a32 in light yellow. In order to do so, I start marking a13 and a23:

[![two coefficients marked to highlight them in the next step][2]][2]

Then I select **Format > Backgrond Color > Light Blue**:

[![Background Color set to light Blue][3]][3]

But nothing happnes. 
Nota bene: The cell onto which I want to apply these operations is editable:

[![cell is editable][4]][4]

**Why can't I add a background color to parts of my printed expression?**

**How can I achieve the desired result which would look like my second picture above, but the text still being black on light blue background?**

**Of course I would also like to use other backfrounds to other parts of my expression too, like e.g. light yellow?**


  [1]: https://i.sstatic.net/gX39T.png
  [2]: https://i.sstatic.net/P33fj.png
  [3]: https://i.sstatic.net/MoKHS.png
  [4]: https://i.sstatic.net/Zbulw.png