Ongoing Sparkplug Problems.. Now Sparkplugs are tinted orange....

[[R]achel]

My VR Exec was recently idling real rough. I bought all new bosch leads and bosch spark plugs and fitted them. Car was running smooth for 2 months with no problems then again it started idling rough again, not as bad this time. Checked all plugs and leads once again, car ran smoothly for a month until I hadto get a new harmonizer installed then 2 weeks later the car idled rough again. Redone plugs and leads for the 3rd time. Car ran smooth for 1 week and now again the car is rough idling bad this time. So yesterday I redone it all for a FOURTH time took it for a drive she drove fine after 5 minutes of driving then when it hit 100k it started making a loud rattling noise through he whole car. I checked all the plugs and the leads today to find that the 1st and the 6th are going orange on the white ceramic outer casing. Also the 1 st one and its lead was black and really dirty on the ouside and the screw in part. Where as the 6th wasn't so black on the outside but it was dirty inside yet the very tip was completly dry and only grey unlike the 1st which was black to the tip.

I have no idea what to do I am now going to buy to new spark plugs ttry if that makes a difference, but I want to know why they keep playing up and will it keep happening... PLEASE HELP ME