Positive vs. Negative
Reversed type, white on black or on any other color, is almost impossible to read in quantity. A statement in reversed type can be readable in a headline or sub-headline, but it must be brief and of sufficient size for the characters to be recognizable. If you want to hide your message, reverse the text.
Why So Many Columns?
Text is set in columns to increase the comfort and speed of reading. The wider the column, the more eye movement required in scanning the text. Most newspapers use columns that are about 26 characters wide and are set in 10-point type. If the text were set to run across two or three column widths, there is a risk of "drop-off," where the reader actually drops off the line due to the effort of too wide a scan.
"Dropping Off" the Cliff...
Drop-off is relative to the length of the text and the size of the type. You can use a wider column as long as the type size is increased to balance the length of the line.
Drop-off is also a factor in designing for the new wider website standard of 1024 x 768 pixel width. Designers should artfully balance artwork, sidebars and navigation columns to avoid a layout that requires the reader to scan the full length of the wider web page.