Your deface override is not working because you're trying to replace content which doesn't exist in the template you're overriding.
Take a look at the source for the template here: https://github.com/spree/spree/blob/v2.2.0/frontend/app/views/spree/shared/_footer.html.erb
I'll paste it below, as it's small.
<footer id="footer" class="sixteen columns" data-hook>
<div id="footer-left" class="columns alpha eight" data-hook>
<p><%= Spree.t :powered_by %> <%= link_to 'Spree', 'http://spreecommerce.com/' %></p>
</div>
<div id="footer-right" class="columns omega eight" data-hook></div>
</footer>
In your deface override, you should see it apply if you change it to override something that is in that template. For example,
:replace => "#footer-left"
If you're just looking to change some of the colours around you should override this file:
You can then redefine some of the variables listed here:
You can also style elements by applying new CSS to them, or override the existing styles with higher priority CSS selectors.