I would agree with making enough of a change that it doesn't appear as a twin. How hard can it be to use a darker or lighter shade for part of it, move something a little forward or down, change the pinstripe color, or even choose a different base color?

The few times I have been asked to copy a job, the owner and I sat down, and tried to determine if we could improve the design. Often, the first attempt has something about it that might not be the ultimate version of their idea. So far we have always found something we felt could be better......so why not have a unique job? The cost is about the same.