Can you, please, detail which exactly color do you mean: the text color? The links color? The background colors of some elements?
Many examples of customizations can be found in our knowledge base
, and this article is the suggested starting point for CSS customization: http://kb.ecwid.com/CSS-Faq
. There are also some ready made CSS themes built into Ecwid, which you can enable at Ecwid control panel > System Settings > Design > CSS Themes. They already contain wide customization over the colors in the shop, so maybe they will inspire you and give an appropriate example.