Fonts Choices Can Not be seen at Night
I'm assuming your Mac is running macOS Sierra or later and your Mac has Night Shift enabled (by default Night Shift will change the appearance of your screen at night).

To access Night Shift settings go to Apple > System Preferences > Displays and select the Night Shift tab (see screenshot below): 



Depending on your version of macOS your Displays preference pane may look slightly different to the image above.

Now you have two options:


Totally disable Night Shift by selecting "Off" from the Schedule drop-down menu
Experiment with the Color Temperature slider (at night with Pages open) to see if you can get it so that your font choices are easier to read.


NOTE: You shouldn't have to reboot for the changes to take effect, but if they don't when you're expecting them to (e.g. you set a schedule from 7pm and nothing changes even though it's already after 7pm), you may need to reboot for the change to take effect.