Does the new color have to be very dark?  

No, the color can usually be changed between color families without going noticeably darker. Some color selections actually can appear to be a lighter color. We can take Light Gray to Light Beige or Light Beige to a Light Gray, a Light Rose to a Light Country Blue or a light Country Blue to a Light Rose, a Gold to a Taupe or a taupe to a Gold and many more. While we can't take a Dark Blue to a Light Green, we can take it to a Dark Green or other equally dark colors. We can make a very slight color tint or make a dramatic color change to another color family. You just have to see it to believe it!