Hello, hydroman,

Good question(s).

Hydra-Matic drive-line colors - 1954 Chevrolet trucks:
235 engine - medium gray (lighter than 1953 and earlier engine-gray, light "Ford" gray - little or no blue in it)
transmission - I think I used the same color as the engine gray
u-joint housing - ??
rear-end (including torque-tube) - ??

Shocks were gray.

Let's hear from other 1954/55st 31xx Hydra-Matic owners? (Greg Hill?)

Do not be surprised by differing opinions.
No one has ever posted GM documents with paint codes (or color names) for those parts.