I'm working on a site which has its main colors as a dark red and carbon fiber as main colors. After an email is sent, a confirmation message is displayed. Would it be acceptable to make this confirmation message in red to match the site colors, or would it confuse people as generally success messages are green and error messages are in red?
User interfaces have over the years established standards to help users recognize common situations. We have come to associate messages with red text, red background or other red elements with warnings about something that has gone wrong.
If you were to present positive messages using the standard presentation of a negative message, in stead of communicating with your users in a way they'll understand, you create for them a Stroop effect test.
Regardless of your site's style, in a user interface you need to be able to communicate failure, success and other messages in an easily understandable way.