I think this about covers it...please correct me if I'm wrong.
Icon Explanation
1/8th megabyte = 1 megabit == 128 kB/s = 1024 kilobits
1.1 Warning Icon - 5 kilobits (0 < 1 kB/s)
1.2 Red - 10 to 100 kilobits (1 - 12 kB/s)
1.3 Yellow - 100 kilobits to 2 megabits (12 - 256 kB/s)
1.4 Green - over 5 megabits (> 640 kB/s)
2.1 Modem / ISDN
2.2 Cable / DSL
2.3 Wireless
2.4 LAN (T1) / LAN (T3)
3.1 Admin / OP
3.2 Red Mine - User has uploaded at constant 100kB/s or above
3.3 User is on a LAN
3.4 Question Mark - No connection info
4.1 Green Check - You have communicated with the user. Can appear over any user (exchanged file lists)
4.2 Red Wall - User is passive or not connectable
4.3 Dimmed Icon - User is away. Can appear over any other user icon
4.4 User is using Net Limiter
Color explanation
