I think I own most of the (known) colors for 2×4 Modulex bricks.
LEGO logo
Early colors (1963)
0 – Mx Clear
1 – Mx White
2 – Mx Light Gray
3 – Mx Black
4 – Mx Terracotta
5 – Mx Buff
6 – Mx Ochre Yellow
7 – Mx Olive Green
8 – Mx Teal Blue
9 – Mx Brown
Later colors (1983-1997)
11 – Mx Pastel Blue
12 – Mx Orange
13 – Mx Red
14 – Mx Pastel Green
15 – Mx Lemon
16 – Mx Pink
M logo
“Legacy” colors:
[MISSING] 10 – Mx Clear
1 – Mx White
2 – Mx Light Gray
3 – Mx Black
4 – Mx Terracotta
5 – Mx Buff
[6 through 9 don’t seem to exist]
Later colors (1983-1997)
11 – Mx Pastel Blue
12 – Mx Orange
13 – Mx Red
14 – Mx Pastel Green
15 – Mx Lemon
16 – Mx Pink
Later M logo (1997-2006)
31 – Mx White
32 – Mx Light Bluish Gray
33 – Mx Pink Red
34 – Mx Aqua Green
35 – Mx Light Yellow
37 – Mx Violet
38 – Mx Medium Blue
39 – Mx Light Orange
40 – Mx Charcoal Gray
Prototypes/tests/unreleased
LEGO logo ABS
Dark Green-ish (?)
LEGO Yellow
LEGO logo, Polystyrene (?, same as waffle plates)
10 – “Strong Red” (same as LEGO Bright Red)
White
M logo, ABS (1983-1997)
[MISSING] Mx Medium Gray (?, 2×2 for reference)
[MISSING] Mx Dark Bluish Gray (?, 2×2 for reference)
[MISSING] Mx Dark Teal (?, 2×2 for reference)
Mx Cyan (?)
Mx Burgundy (?)
Other bricks missing:
CA Black, Red, White, Blue and Yellow.
2014 Black test (do other colors exist?)
Bonus: Bricks with painted studs.