My african mantis nymph has just shed and gone a very dark colour.Is this normal.

dark colour as in brown? Mantids will change colour during moults its the only time they can. Depending on the environment its been kept it, if your environment is far different to the suppliers then that would likely be the case.

A picture would help decide if its something to worry about but I dont think it will be.

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1.1.0 Western Hognose '06
1.0.0 Banana Kingsnake '06
1.0.0 Ghost Corn '03

0.0.2 African Mantis (Sphodromantis lineola)
1.1.1 Ghost Mantis (Phyllocrania paradoxa)
0.0.4 Madagascan Marbled Mantis (Polyspilota aeruginosa)
0.0.3 Pnigomantis medioconstricta

it looks healthy and its eating.
i was just alarmed because it was grape green yesterday.

Yeh dont worry its normal mate. Mine just shed and have taken a stunning camo-effect. Interesting to see

__________________
1.1.0 Western Hognose '06
1.0.0 Banana Kingsnake '06
1.0.0 Ghost Corn '03

0.0.2 African Mantis (Sphodromantis lineola)
1.1.1 Ghost Mantis (Phyllocrania paradoxa)
0.0.4 Madagascan Marbled Mantis (Polyspilota aeruginosa)
0.0.3 Pnigomantis medioconstricta

Thats exactly what mine looks like.Just wanted to check because its my first mantis and wasnt too sure.cheers