(Fellow semi-beginner's response:) I tried this with the different ways of viewing text available to me on the mac with no problem. I notice the LyX manual says, discussing the text styles dialogue, (3.6.4):
Color: You can adjust the color of the text with this control. Notice that not all dvi-viewers are are able to display colors. ... Then googling Yap color text I promptly got http://www.gnustep.it/marko/GPSText/index.html saying: Getting colored output: Set "PostScript Device" to "24 bit color" for color previews; use the style sheet "color" to get colored a2ps output. This only works if the color style sheet is installed on your system ("/usr/bin/a2ps --list=style-sheets"). Note that mutally contradictory options to a2ps may cancel each other out. So it looks like its to do with Yap, which is bundled with Miktex. It would probably be easiest to set something else as a viewer, through the general LyX preferences: Preferences --> File Formats --> DVI then look whats listed as the viewer - and try to change it. I don't know what else you may have to view it, but there is plenty about this sort of thing if you search these posts, for example.
