Strange spark plug color
 

3.0 liter v6.

So what started this is a slow loss of coolant. I still resolved that problem. IT could be a slow leak somewhere that is evaporating and I haven't found it yet. But I have pulled all the plugs and also did a compression test.
I have never seen this coloration on plugs before. Half the plug is clean and white. The other side is a normal burn color.

One cylinder has 110 after 3 turns. 135 after many turns. It is about 20 lbs lower than the other cylinders. That cylinder also has the darkest plug color. I am not sure I should worry about the compression but I am trying to find the coolant issue. If the head have to come off for the coolant, I am fine with that. But if it is a leak somewhere else, I am not worried about the lower compression in one cylinder unless of course it gets worse.

Anyone ever see plugs as I described? They all seem to have one side a lighter color than the other side. Two adjacent plugs plugs have that coloration issue. Makes me wonder if the head gasket is leaking there, but the compression is really good as I stated.

Anyone have an explanation?

(I am still going to look for a leak).

For others, compression should be within 10 percent of all cylinders for the engine to run really smooth. Plugs which get a shot of coolant will appear very clean, white and little deposits will be present.A cracked head into the comustion chamber or head gasket issues will cause send high pressure combustion gasses into the cooling system, the coolant bottle likely will fill up and could overflow.