An easy way to add Three.js to Blogger is to embed a Three.js page as the source in an IFRAME.
And you can even edit the code in the post causing the animation to update.
For example, change camera.position.z to 800 or color: to 0cff0000.
Here's the code for the iframe that causes the Three.js online editor to appear here.
<iframe height="40%" src="http://mrdoob.com/projects/htmleditor/" style="border: medium solid rgb(0, 0, 0);" width="100%"></iframe>
It's best to keep the iframe height well under 100%, otherwise the frame can obscure your code while you are editing the post.