After some trial & error, I've come up with the following dark theme for TeXstudio, using (mainly) colours from the Solarized colour palette; thanks to @Holene for recommending the latter to me.
I'm conscious this kind of tweaks is very much a matter of taste, and may not appeal to anybody else than me. However, my colour settings might be helpful to someone who wants to set up a dark theme in TeXstudio. Therefore, I've decided to post them as an answer; see below.
To apply those setting, substitute the following code for the code currently under the "[formats]" heading in your TeXstudio settings file (.txsprofile); then load that settings file in TeXstudio. You will have to restart TeXstudio for the changed to be effective.
Edit: (shameless plug!) Incidentally, I've released a tiny package, called xcolor-solarized, that simply defines the 16 colors from Ethan Schoonover's popular Solarized color palette, for use in documents typeset with LaTeX & friends. It has been released on CTAN; development takes place on GitHub.
[formats]
version=1.0
data\normal\priority=-1
data\normal\bold=false
data\normal\italic=false
data\normal\overline=false
data\normal\underline=false
data\normal\strikeout=false
data\normal\waveUnderline=false
data\normal\foreground=#839496
data\normal\fontFamily=
data\normal\pointSize=0
data\background\priority=-1
data\background\bold=false
data\background\italic=false
data\background\overline=false
data\background\underline=false
data\background\strikeout=false
data\background\waveUnderline=false
data\background\background=#002b36
data\background\fontFamily=
data\background\pointSize=0
data\commentTodo\priority=-1
data\commentTodo\bold=false
data\commentTodo\italic=false
data\commentTodo\overline=false
data\commentTodo\underline=false
data\commentTodo\strikeout=false
data\commentTodo\waveUnderline=false
data\commentTodo\foreground=#6c71c4
data\commentTodo\fontFamily=
data\commentTodo\pointSize=0
data\comment\priority=-1
data\comment\bold=false
data\comment\italic=false
data\comment\overline=false
data\comment\underline=false
data\comment\strikeout=false
data\comment\waveUnderline=false
data\comment\foreground=#586e75
data\comment\fontFamily=
data\comment\pointSize=0
data\keyword\priority=-1
data\keyword\bold=false
data\keyword\italic=false
data\keyword\overline=false
data\keyword\underline=false
data\keyword\strikeout=false
data\keyword\waveUnderline=false
data\keyword\foreground=#cb4b16
data\keyword\fontFamily=
data\keyword\pointSize=0
data\extra-keyword\priority=-1
data\extra-keyword\bold=true
data\extra-keyword\italic=false
data\extra-keyword\overline=false
data\extra-keyword\underline=false
data\extra-keyword\strikeout=false
data\extra-keyword\waveUnderline=false
data\extra-keyword\foreground=#859900
data\extra-keyword\fontFamily=
data\extra-keyword\pointSize=0
data\math-keyword\priority=-1
data\math-keyword\bold=false
data\math-keyword\italic=false
data\math-keyword\overline=false
data\math-keyword\underline=false
data\math-keyword\strikeout=false
data\math-keyword\waveUnderline=false
data\math-keyword\foreground=#268bd2
data\math-keyword\fontFamily=
data\math-keyword\pointSize=0
data\link\priority=-1
data\link\bold=false
data\link\italic=false
data\link\overline=false
data\link\underline=true
data\link\strikeout=false
data\link\waveUnderline=false
data\link\fontFamily=
data\link\pointSize=0
data\align-ampersand\priority=-1
data\align-ampersand\bold=true
data\align-ampersand\italic=false
data\align-ampersand\overline=false
data\align-ampersand\underline=false
data\align-ampersand\strikeout=false
data\align-ampersand\waveUnderline=false
data\align-ampersand\foreground=#dc322f
data\align-ampersand\fontFamily=
data\align-ampersand\pointSize=0
data\verbatim\priority=-1
data\verbatim\bold=false
data\verbatim\italic=false
data\verbatim\overline=false
data\verbatim\underline=false
data\verbatim\strikeout=false
data\verbatim\waveUnderline=false
data\verbatim\fontFamily=
data\verbatim\pointSize=0
data\sweave\priority=-1
data\sweave\bold=false
data\sweave\italic=false
data\sweave\overline=false
data\sweave\underline=false
data\sweave\strikeout=false
data\sweave\waveUnderline=false
data\sweave\fontFamily=
data\sweave\pointSize=0
data\picture\priority=-1
data\picture\bold=false
data\picture\italic=false
data\picture\overline=false
data\picture\underline=false
data\picture\strikeout=false
data\picture\waveUnderline=false
data\picture\foreground=#c93682
data\picture\fontFamily=
data\picture\pointSize=0
data\numbers\priority=-1
data\numbers\bold=false
data\numbers\italic=false
data\numbers\overline=false
data\numbers\underline=false
data\numbers\strikeout=false
data\numbers\waveUnderline=false
data\numbers\foreground=#2aa198
data\numbers\fontFamily=
data\numbers\pointSize=0
data\math-delimiter\priority=-1
data\math-delimiter\bold=true
data\math-delimiter\italic=false
data\math-delimiter\overline=false
data\math-delimiter\underline=false
data\math-delimiter\strikeout=false
data\math-delimiter\waveUnderline=false
data\math-delimiter\foreground=#399900
data\math-delimiter\fontFamily=
data\math-delimiter\pointSize=0
data\text\priority=-1
data\text\bold=false
data\text\italic=false
data\text\overline=false
data\text\underline=false
data\text\strikeout=false
data\text\waveUnderline=false
data\text\fontFamily=
data\text\pointSize=0
data\escapeseq\priority=-1
data\escapeseq\bold=false
data\escapeseq\italic=false
data\escapeseq\overline=false
data\escapeseq\underline=false
data\escapeseq\strikeout=false
data\escapeseq\waveUnderline=false
data\escapeseq\fontFamily=
data\escapeseq\pointSize=0
data\latexSyntaxMistake\priority=-1
data\latexSyntaxMistake\bold=false
data\latexSyntaxMistake\italic=false
data\latexSyntaxMistake\overline=false
data\latexSyntaxMistake\underline=false
data\latexSyntaxMistake\strikeout=false
data\latexSyntaxMistake\waveUnderline=false
data\latexSyntaxMistake\fontFamily=
data\latexSyntaxMistake\pointSize=0
data\environment\priority=-1
data\environment\bold=false
data\environment\italic=false
data\environment\overline=false
data\environment\underline=false
data\environment\strikeout=false
data\environment\waveUnderline=false
data\environment\foreground=#b58900
data\environment\fontFamily=
data\environment\pointSize=0
data\structure\priority=-1
data\structure\bold=true
data\structure\italic=false
data\structure\overline=false
data\structure\underline=false
data\structure\strikeout=false
data\structure\waveUnderline=false
data\structure\fontFamily=
data\structure\pointSize=0
data\current\priority=-1
data\current\bold=false
data\current\italic=false
data\current\overline=false
data\current\underline=false
data\current\strikeout=false
data\current\waveUnderline=false
data\current\background=#073642
data\current\fontFamily=
data\current\pointSize=0
Tex file was taken from 
.tmThemeor port it to.texsprofile?