Forum Moderators: goodroi
The meta keywords tag is not important to most search engines anymore. They prefer to look at the text on your page. Make sure any keyword you want to rank for can at least be found in the text.
I personally would not spend time on meta keywords but instead I would focus on content and links, links and more links. If you still want to go ahead you should enter it like "blue widget, red widget, big widget, small widget".