What is the problem? Is there any Lua errors?
As the titles states the player castbar doesn't change color for successful casts (by default green). However, target and focus target castbars do.

Console doesn't print any errors

What steps will reproduce the problem?
Just conduct a cast

Does the issue still occur when all addons except ClassicCastbars are disabled?
Yes

Is this for Classic or TBC client?
TBC

Any additional info? If you play on a non-english client, please include your locale type:
En client