Modulex started out in 1963 with earthy colors for architectural planning. Modulex broke off from TLG and became its own company in 1965, but the “LEGO”-logo molds were used until around 1983, when the Plancopy system was introduced.
Plancopy brought new molds, with “M” on the studs. There was a very short period of overlap around 1983; all LEGO-logo colors and early M-logo colors were briefly available in both colors, at least in a few brick types.
Sometime around 1993/4, Modulex’s “Interior 10 Signage System” was changed to include the “Tile – ” colors. These were only available in tiles, with letters or numbers in various sizes (2-tall, 4-tall, or 8-tall).
In 1997, Plancopy was updated, and the majority of the existing colors were replaced with brighter, more vibrant colors. These colors are the rarest, apart from the “Tile -” colors.
Note that many of these dates are best-guess estimates, especially the more recent ones. It’s surprisingly difficult to find concrete information about the history of Modulex.
[Original post and comments on Flickr.]