The reason you cannot find color blind modes on Fortnite mobile on both android and IOS is because Fortnite haven’t added it.
They haven’t added it because both android and IOS both have color blind settings in the main mobile settings. So, there was no reason for Fortnite to add them.
You just must make sure that you set the android or IOS color blind mode to the same one you use on Fortnite.
If you don’t know how to set color blind mode on your specific device then a quick google search should solve your issues.