Re-using a customized theme

Here’s another newbie question…

I’ve adopted one of the themes that have been published by those excellent designers and have tweaked it by changing colours and other elements including the sidebar, so it’s Goldilocks “just right” for me now.

So, now I want to use my customized theme to create a new blog. What’s the best way to do that?

I don’t want to start over and make all the changes to the standard theme again.

Is there a convenient way to re-use this costomised theme that I’m using now?