NiZn ferrites have a brown streak, MnZn black.
To observe the streak, take a file, sandpaper, abrasive stone, etc. to the material and make some dust.
NiZn ferrites have lower saturation flux density, lower permeability and higher frequency range than MnZn. NiZn are used for RF applications while MnZn are used in general purpose and power applications. Both are used in ferrite beads for respective bandwidths.
Getting more specific than this, I think, involves actually measuring the thing. Example: a #77 ferrite inductor will have a very low Q at 10MHz, while a #61 will have a high Q.
Tim