Cascading Style Sheets, or CSS, will let you do this. Basically, as a web designer, you really should be using this anyway - the likes of the <font> tag is now redundant.
Simply, you create a seperate file (I normally call it 'default.css') with your styles, classes and ID's (read a tutorial for all that) and put a little link in the <head> section to the file.
<link rel="stylesheet" src="default.css" type="text/css"
No need for the <font> tag anymore, as anything in the <body> will be exactly as was defined in the stylesheet.
If it sounds complicated, it really isn't. So long as you know a bit of HTML, the idea and philosophy behind it won't be too bad. There are loads of tutorials avaliable on the net, but I quite like the various tutorials at
www.webmonkey.com and
www.elated.com