V8 350 question

[R@nger]

I've brought my 350 small block a long ways since when I got it a year ago. When I got it, it ran horribly but after a good bit of work it seems to be running really good now however I have a question. It wasn't until about, mmm 1-2 weeks ago that my truck saw road time since I got it. I took it to get exhaust and to get emissions tested. Anyways I decided to pull the plugs and found something kinda weird. I started taking them with the right one ad working my way back. The first 3 were all tan and looked good but the last spark plug on the right side was a little blacker. I made a mental note then proceeded to take out the left side spark plugs. The first plug was one that was older than the others because I broke the previous one. It was a little blacker than I wanted it but not horrible. The middle two again were tan, but the last one was noticably blacker than the previous ones on the left side. I started wondering what might have cause this. Any ideas? Could the timing be off?..., I'm thinking it's something either with the timing or its something electrical.

Any help would be awesome, thanks!