"Justify text fully": heavens, why? It might make some designs look prettier at first glance, but all the research that I can recall suggests that it makes it the text harder to actually read, at least the way that the algorithms in web browsers do it...
Because I find justified text easier to read, mostly. I think this depends strongly on the length of the lines: if lines are long enough that any extra space added to justify the lines is a small fraction of the line length then it's easier to read, but as the line length shortens justified text becomes harder and harder to read.
This reminds me of another rule of thumb I use sometimes: if lines of text are long, increase the inter-line spacing because this makes it less likely that when the reader's gaze flies back at the end of a line it will alight on the wrong line next.
I have an awful time reading light-on-dark unless I increase the size.
Another vote against my colour scheme then? Every time I come up with one I like and which I find easy to read, everyone hates it...