The skin should re-color for you using the Colours tab in the windowblinds config window. However, sometimes the start panel won't re-color...especially if it is a really dark skin. Your only option then would be to open the skin in Skin Studio, and re-color it from there. You could also PM the author of the skin and ask if that person would recolor it for you.
What is the name of the skin you are talking about?