With a clean install with Forge 1492 and the latest release of Werkbench, 1.2.56:

I've experienced this issue with EasyCrafting and Steve's Production table as well...

Odd, and that's with no other mods installed at all? Just Werkbench, nothing else?

Yeah; not sure what's causing it. On the Production Table issue, "add getColor can fix this issue" was posted by someone. Maybe that helps?

https://github.com/loldudester/EasyCrafting/commit/e0a3cab3173ab65f658dbe1cbcec6c2855475b99

The issue was fixed in EasyCrafting, could you possibly do the same to Werkbench?