If you're referring to Standard UP 1.4, it may be related to graphics acceleration and windowed mode. If you are using windowed mode, try disabling it. If you aren't using windowed mode, try enabling it from the installer. To disable windowed mode and use fullscreen mode like v1.0c, you can reinstall with the "Windowed mode support" checkbox unchecked, or use the "NOWND" shortcut parameter, or delete "wndmode.dll" in the "age2_x1" folder.
If you're referring to Voobly, try toggling 32-bit color mode in the game room options.
If you're referring to Voobly, try toggling 32-bit color mode in the game room options.