What color wallpaper makes page control dots on iPhone invisible?
You can't make the dots completely invisible.

The iOS SpringBoard (or Home screen as it is generally called) is programmed such that the Page Controls (dots) which appear just above the Dock remain legible irrespective of the colour of the wallpaper in the background. This is done by assigning them colors which are in contrast to the colour of the background.

The logic ensures that at-least the colour of the dot representing the current page of Home screen is most clearly visible.

There is no publicly available official document to back this fact. The conclusion can be reached by performing a small experiment as described:


Set the background to solid #000000 or RGB: 0, 0, 0 (Black color).





Get the color code for the Page Control dots corresponding to non-current screens. Notice the colour code for the dots. The value is #727374 or RGB: 114, 115, 116.





Create a solid colored background image of resolution equal to that of iPhone's screen (640 x 1136 in my case, iPhone 5s), with the above noted color code and assign it as iPhone background. The color code was picked corresponding to non-current screen dots as they can have more than one instances.





Now once again, get the color code for the Page Control dots corresponding to non-current screens. It can be observed that the colour for the dots has changed.





Now, create a solid colored background image with colour code #FFFFFF or RGB: 255, 255, 255 (White colour). Once again, notice the color of the dots. The color corresponding to the current screen has changed from White in first image to Black in the current image.






P.S.: I have played around a lot with both macOS and iOS to minimise eye-candy by working through such tricks. Above conclusion is just an observation without any documented backing from Apple. The attached iPhone home screen screenshots have been scaled down to 50% of their original resolution.