Color of Leaky Electrolyic Caps?

[Marvin Johnston via cctalk]

I was just checking out the leaky capacitors on the model 100 
motherboard, and they are all colored black. And ditto for the HX-20. 
The ones that are both light and dark blue look to be fine (no leakage.)

So am I just seeing an anomaly, or is this the experience of most people 
here?