How to make the Tumblr blog hide the source

If you have too many, I would say go for google-code-prettify.

All you have to do is to include some javascript, css and then you're done.

Check some examples and here is the setup:

1. Download a distribution
2. Include the script and stylesheets in your document (you will need to make sure the css and js file are on your server, and adjust the paths in the script and link tag)
   • <link href="prettify.css" type="text/css" rel="stylesheet"/>
   • <script type="text/javascript" src="prettify.js"></script>
3. Add onload="prettyPrint()" to your document's body tag.
4. Modify the stylesheet to get the coloring you prefer

Include the following code:

{block:HasTags}
   {block:Tags}
       <a class="tag" href="{TagURL}">{Tag}</a>
   {/block:Tags}
{/block:HasTags}

in the block for each type of post. So you will have this seven times: in {block:Text}, in {block:Audio}, etc.

Put this right before the closing of the block (so right before {/block:Text}, for example) to have the tags show up at the end of the post.

Tumblr provides some documentation on this here.