Step 1: Go to Settings
When you're at the settings, scroll down to the tab that says General.
Step 2: Accessibility
Once you're at the General settings, scroll all the way down to Accessibility.
Step 3: Permanent Invert Colors
Find the tab that says Invert Colors with an on/ off switch and change that over to ON.
(Not totally permanent forever but more permanent than the second option)
Step 4: Temporary Color Switch
Scroll all the way down until you see the tab that says Triple Click Home. Once you press that, press the tab that says Invert Colors.
(Make sure that it shows a checkmark next to Invert Colors)
Step 5: Checked Off
Step 6: Triple Click Home
Go back to the home screen and to invert your colors press the home button three times fast to invert colors and three times fast to go back to normal.