A newbie question in XSL - Using variables

Hello;

I have a simple question that Im trying to solve:

<xsl-if test="some condition">
           <font color="red"> Hello 1</font> 
</xsl-if>
<xsl-if test="some other condition">
           <font color="blue"> Hello 1</font> 
</xsl-if>

Now, is there a way to obtain the above criteria something like,

<xsl-if test="some condition">
           $somevariable = "red";
</xsl-if>
<xsl-if test="some other condition">
           $somevariable = "blue";
</xsl-if>
<font color=$somevariable> Hello 1</font> 

I understand that I cannot use <xml:param> and <xml:variable> as they are constants. Please let me know a solution to this trivial problem.

Thanks,
Prasanna