The Razer Blade 15 along with some other performance laptops suffer this strange issue that when going from a dark image to a light image the laptop decides to dim or brighten the screen.
The fix for this is to change "Enable adaptive brightness" to off. - change it for both battery and when plugged in.
The setting is found in Control Panel > Power Option > Change advanced power settings > Display
Turn both options to off
If that doesn't work another option is to turn off "Display power saving technology".
This setting can be found in the Intel UHD Graphics Control Panel > Power
Change it for both "On Battery" and "Plugged In"