It has been a very long time since I was super into car stuff, but IIRC brown like this is indicative of the plugs being too cold in general, but color is more to do with a short term diagnostic method of tuning.

In this case, from the image angle, it looks like way too large of a gap. You probably need to look into setting your gaps. The new plug is likely closer to a decent gap. The older plug looks like it was intended to be gapped manually but never was.

Also, limited by the angle of the image somewhat, but it appears that the plug was only firing from a single hotspot. Those pointy corners of the tab are intended to focus the spark into one area for a more reliable ignition timing and flame front propagation. However, this engineering methodology tends to cause a deposition of material at this point location over time. This plug clearly has a considerable build up of material around this hotspot. That build up could have caused the plug to fire cold and late in the cycle thus building up the brown deposit on the ceramic insulator.

The new plug is of a better design for long term use without service. The rounded sharp edges (on both sides of the spark) will allow the spark to propagate from more places along that edge after any specific hotspot builds up resistance. It has less predictable flame front control, but this does not matter on most factory vehicles, just racing and motorsports really.