The Bueno theme does not have the option of "hiding" the blog title here > Appearance > Themes > Header If you remove the blog title form here > Settings > General then the search spiders will not locate it and they will not index your blog. You can change the font family with TypekIt fonts but you cannot change the color or size.
Your only other options for "Changing Blog Title Size and Font" are to change themes to one that does have the "hide text" feature which is free of charge. Or to purchase an annually renewable CSS editing upgrade and do the work yourself.
If you have CSS editing experience, you can get the paid custom CSS upgrade and renew it annually. It will allow you to stylize the appearance of themes you find here > Appearance > Themes, but it does not allow you to change the functionality, by editing the underlying template. It does not allow you to remove footer links to the theme designer or to wordpress.com. Also note that CSS is theme specific, so you cannot use the CSS stylesheets from other themes with the themes here at wordpress.COM.
Since there is no official Staff support for the CSS upgrade, and precious little Volunteer support, I recommend that you don’t buy the upgrade unless you have at least moderate understanding of HTML and CSS because you must be prepared to do the work on your own.
If you are considering purchasing the upgrade, you can go to Appearance > Edit CSS. There wordpress has provided a preview function where you can try before you buy.
If you do purchase the upgrade be sure to read this article before starting your editing > http://csswiz.wordpress.com/2009/10/15/if-you-have-the-wp-com-css-upgrade/