<xsl:template match="your-html-element">
    <div class="color-every-other">
        <xsl:variable name="content" select="path-to-content"/>
        <xsl:for-each select="tokenize($content, ' ')">
            <xsl:choose>
                <xsl:when test="position() mod 2 != 0">
                    <span><xsl:value-of select="concat(., ' ')"/></span>
                </xsl:when>
                <xsl:otherwise>
                    <xsl:value-of select="concat(., ' ')"/>
                </xsl:otherwise>
            </xsl:choose>
        </xsl:for-each>
    </div>
</xsl:template>