Unipolar motors can be almost as easy to diagnose.
Measure the resistance from each phase and make sure you have the right wire for the common. Orange to white should give you the same resistance (give or take a bit of an ohm or so) as the white to blue wire. Same again with the red to black and yellow to black wires.
That only leaves you with 4 wires to incorrectly connect
You won't break anything by trying different combinations of those wires.
Something else you might want to try is to put an LED between each phase and ground or live depending on how you're driving the common and obviously with a current limiting resistor. That way you can watch which phase is activated and compare it with the step chart in the datasheet.