To reverse the spin direction of a sensorless brushless motor with three wires colored red, blue, and black, you simply need to swap any two of the three motor wires. It does not matter which pair you choose. Swapping the red and blue wires, or the red and black wires, or the blue and black wires will reverse the phase sequence, which makes the motor spin the opposite way.
This works because sensorless brushless motors do not have Hall effect sensors that would need recalibration, so you are only changing the power wires. Trying different combinations will not damage the motor or the controller. If the motor spins the wrong way, just swap a different pair. If the motor does not spin at all after swapping, some electronic speed controllers require recalibration after changing wiring. If the motor stutters or jerks, that usually indicates a poor connection or a damaged ESC or motor. The colors on the wires are just identifiers and carry no fixed polarity.
The bottom line is swap the red and black wires first. If that does not work, try red and blue. One of those pairs will get you spinning in the right direction.
If your motor is sensored (meaning it has additional small wires — usually 5 or 6 — for Hall effect sensors in addition to the three thick power wires), swapping any two of the three thick power wires alone will not reverse the direction properly.
With a sensored brushless motor, the ESC relies on position feedback from the Hall sensors to know exactly when to fire the windings. If you simply swap two power wires without also swapping the corresponding sensor wires, the ESC becomes confused. The timing will be wrong. The motor may stutter, refuse to start, draw excessive current, run very rough, or not spin at all. To correctly reverse the spin direction, check if your ESC has a programmable reverse function. Many sensored ESCs, especially those used in RC cars and robotics, allow you to reverse the motor direction through software, a programming card, or a SET button without touching any wires. This is the cleanest method and is highly recommended if available.