These are our realities at wordpress.com when it comes to changing font colors and sizes:
(1) Changing font families, colors and size in text in posts or pages either post by post or page by page by coding into the HTML editor. http://en.support.wordpress.com/editors/font-size-color/
(2) Changing font colors in text in posts or pages either post by post or page by page using the #4 icon (Select text color – change the text color) in Row 2 the Visual editor. http://en.support.wordpress.com/visual-editor/#row-2
(3) Changing all font families, colors and sizes throughout the whole blog by purchasing an annually renewable Custom Design upgrade and using Typekit Fonts with Staff support. http://en.support.wordpress.com/custom-design/
Note: A few themes do provide for changing font color in the Blog Title and/or optional Tagline and/or links. In the majority of themes font changes to font families, colors and size in the blog title, tagline, menu, post titles, page titles, categories and tags, widget headings, leave a comment, comments, and links cannot be done without CSS editing.