Changing Testimonial Text Colour

Hello,

I'm trying to change the colour of the testimonial author to #fff here: http://us17.siteground.us/~oddsonic/allegria.ca/#testimonials

I thought this CSS would do the trick, but it's not working:
.mk-testimonial.avantgarde-style .mk-testimonial-author {
color: #ffffff !important;
}

Thanks in advance,
Casper