Hello julie-anne98,
From your post it appears your iPhone is only showing grayscale.
Just to confirm, when you tap on Settings > Accessibility > Display & Text Size > Color Filters is set to Off. Be sure that both Smart Invert and Classic Invert are also toggled off.
If Color Filters is already set to Off, go ahead and tap on it, tap on Color Filters, choose something other than Grayscale, then toggle back to Grayscale. Toggle Color Filters off.
Also check Settings > Accessibility > Zoom and check the Zoom Filter. Make sure it is set to None rather than Grayscale.
More information on this settings are available here: Get started with accessibility features on iPhone - Apple Support
Have a good day.