Hey guys, i have a question. I'm looking to buy a 1983 Marshall JCM800 2203 Superlead, and I've figured everything out except one thing. What is the difference between the blue can capacitors and the black can capacitors? There are also some more metallic looking blue ones, are they different from the light blue ones? Here's some pictures to show you what I mean:

I'm leaning towards the light blue ones (last picture) but thats because they are the ones I've heard the most about.

The original early JCM800 caps were the light blue Daly capacitors. They are good to have and sought after. Later on Marshall switched to LCR capacitors which can be dark blue or light blue. These two types are now discontinued.
I have also seen the metallic blue, metallic green, black, and grey caps.
As long as the caps are in good shape it shouldn't matter too much what brand they are out of the ones Marshall used. The number of filter caps is more important. I would rather have to replace 6 caps then have an amp with only 2 original caps. In other words, an amp with 6 caps will always have 6 caps, even when they need to be replaced 100 years from now and so on. An amp with two caps will always have two caps.
So when looking at an amp, count the number of caps. IMO, 6 is the best. If they are original and still working well then that much the better. I hear Sozo & JJ makes a good replacement 50/50 cap. The guys at plexipalace.com will be able to help out a lot as well.