Originally Posted by: oscampo 
It's not possible change the background color of description region.
As explained so many times, Web Master keeps deleting collaboration.
Obviously, on closing Windows, backgrounds aren't saved.
What you show is the white default background.
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Originally Posted by: Soczawa 
Thanks Jean. I think we misunderstood each other. I was proposing to change the background of the description region/field, rather than the input region, as your example shows. Something like this:
In CAS, many math codes aren't commutative.
Samth is not commutative wrt Windows. Windows comes first.
Background is a Windows tool, that you specify before called by Smath.
Specify your collection of backgrounds, click on the one you want your
next description background, plug your math region, show description.
Bingo, your description has your selected background.
Select another background, another math region, description
as desired ... all that in the direction of the commutativity.
1. open Smath
2. define background colors from Smath icon
3. click on the one you want description background
4. compose math region
5. show description ... text.
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click another background, math region, show description.