less --global-var seems not working - less

Question

I'm using less in a JEE project. Compiling less files is via an ant script.
I want to generate multiple versions of bootstrap (and some others less files) with a different color scheme.
So, my script have some :
<antcall target="lessfile">
<param name="file.name.less" value="bootstrap.less" />
<param name="file.name.css" value="bootstrap-orange.css" />
<param name="brand-primary" value="#F44336" />
</antcall>
At the end of the script, I launch compilation via the line:
<arg line="-x ${file.name.less} ${dir.css}/${file.name.css} --global-var='my-background=${brand-primary}'" />
This command line itself poses no worries. The problem is to retrieve the value of 'my-background'.
In the bootstrap file, I do a simple test:
.test {
color : #my-background;
}
And the compilation fails, stating that he does not know the #my-background variable ("variable # my-background is undefined"), as if the argument specifying the global variable was ignored.
Can you explain to me how I can get my global variable value?
Thank you in advance for your answer.
(PS : i have lessc 1.4.2 )