I agree with @jdsilva
When the light is on in the room it'll likely switch back to color.
The camera detects scene light levels using a dedicated sensor. This sensor detects ambient light levels or light directly falling on the camera. You can see two different scenarios of this not working as you would expect.
Adjusting the thresholds or manual fixing night mode transitions will fix both these scenarios.
I have this same issue but have messed with the night mode settings and even disabled night mode and still getting black and white during the day. the camera is a MV21 with Firmware 3.30