The 2X4 brick in its first version (2X4vs01) as well as its companion 2X2vs01, were produced in an extraordinary array of colours. These are the ones represented in my collection of early LEGO material. I avoided the many shades to concentrate on the better distinguishable "average" colours.

From top right to left:

-light yellow (there was also a milky yellow, slightly transparent, as used only in the very first LEGOs, that is very distinctive but hard to document with a scanner), "normal" yellow (the colour used into the later versions of the brick), orange-yellow, orange, "normal" red, dark red, light gray blue, gray blue, azure (there is also a milky azure, as used in the very first LEGO sets), "normal" blue, dark blue;

-greyish green, light green (an odd colour still used when mold vs02 started operation); medium green, "normal" green; dark green (a milky shade of this green was used in the first LEGO sets), white (a very distinctive milky shade of white was used in the very first LEGO sets), transparent cream, transparent gray (these look very similar under the scanner but are distinct, marbleized (this is more of an oddity than a colour! There are many variants.

The last two bricks are from 2X4vs02a molds and are a distinctive blue-based marble and a deep brown. Both must also have been molded on vs01 molds.

IMPORTANT NOTE: In the first issues (from 1949 to 1951? here called "early colours") the bricks were molded with a catalin-type thermoset resin and are transparent against a soft light, even in the darkest colours. Later bricks may, or may not been molded with a thermoset (they respond differently to the transparency test) but the material was never again the same in terms of gloss and high transparency.