I am relatively new to Blender and am doing Andrew Prices' tutorial on Youtube for "Make a Grassy Meadow". I am at minute 44:25 where he flips the mist cube upside down. Unfortunately for me when I flip my cube the gradient remains the same, with the fade ending at the bottom. Does anyone know how to work around/ fix this?
It’s likely that you have ‘flipped the cube upside down’ in Edit mode. This will leave the coordinate mapping unchanged. Instead, ensure you’re in Object mode before trying to flip it.
For something simple like this, I would just separate the generated coordinates into XYZ and use the Z value plugged into a ColorRamp node. This will give you a far better control of your scattering density.
The object orientation should be world oriented (at least if you're using Generated or Object coordinates), so that the Z axis is aligned to the world Z axis. On the right 3DViewport you can see that the local axis for the box has at least the Z axis (blue arrow at the center of the box) aligned with the world Z axis (the blue arrow at the bottom left corner of the viewport). The Z axis is then used from the 'Generated' coordinates, which are mapped from the bottom/top to a scale of 0 to 1 and plugged into a color ramp, that defines the vertical density map.