Hi walelignmessele
According to the code:
reprojection = frame_rgb.copy()
reprojection = cv2.line(reprojection, tuple(p_0[0]), tuple(p_x[0]), (0, 0, 255), 5)
reprojection = cv2.line(reprojection, tuple(p_0[0]), tuple(p_y[0]), (0, 255, 0), 5)
reprojection = cv2.line(reprojection, tuple(p_0[0]), tuple(p_z[0]), (255, 0, 0), 5)
Color is passed in BGR format, so x is red, y is green and z is blue (also it's the usual color coding).
Coordinate frame for the camera should be (i believe) defined by z - positive depth, x - width, y - height (left hand).
But they are not dependent on one another - one is defined inside the calibration script, and the other one is arbitrary.
IMU CS is another story and is defined by the IMU component (the MEMS accelerometers i believe) and its orientation. The orientation should be visible on the PCB assembly pictures.
Hope this helps,
Jaka