First, make sure it is not "Reichspost" #64.

Then, difference of 79 and 82 is:
#79 has gothic script in the bottom panel
#82 has latin script
#82z has frame of #82 but center is like #79.

I would not use color as the main criteria, due to shades, fading and
color changes over time.
Get some (or compare with) some other copies of 79, 82A/B and 95A/B to
get a good feel for the differences.

It is best to get it expertized.





In article ,
(UStamps 4U) wrote:

The 1902 Issue Deutches Reich "Nord und Sud" Union of north and south 2 Mark
stamp with unwatermarked paper is listed in Michel's catalogue with 4
varieties
#79, 82A, 82B, and the rare 82Z. The first three are dark blue (stahlblau).
Only 82Z is listed as blue (blau).
I have one that is unwatermarked, Blue (not dark blue), perf 14.4 x 14.1 all
this leads to being a rare 82Z. But the illustration in Michel's shows the
rays in the sky to be long radial lines similar to 79 except with occasional
breaks. The stamp I have has horizontal dashes very strongly engraved making
up the rays. The engraving is very strong and different from 82A or 82B. I
find this to be unlisted by Michel and need help to confirm the proper
listing.
Thanks for your help.