Here is a spark plug chart.
How To Read Spark Plug Color
The porcelain/ceramic was damaged due to not using a spark plug socket with internal rubber cushion. A standard deep well socket does not have this.
I do not think anything is wrong with the plug. In fact it may be the best of 4.
Replace with similiar Bosch copper plug or NGK cheap copper. No platinum types.
You should do a compression and leak down test on the engine to see if you have worn rings.
Compression-leakdown test
A compression test with an allowance of 10% among cylinders is good. Reading should be about 145 or close on all 4.
Remove the DME/fuel pump relay on the compression test.
GL
John