how to change the space bar color on my iPhone's keyboard?

Thanks for the screenshot!

To my knowledge, you cannot change the color of the cursor. However, you can ask Apple for this feature here: Product Feedback - Apple.

In the meantime, please go to: Settings > Accessibility > Display & Text Size > Color Filters. Now, ensure that the switch next to Color Filters is turned OFF.

Also, as I see you have Dark Mode enabled, you may want to turn it off for now, if you don’t mind, that is. That will give you a black cursor on a white background, which is a 100% contrast.

To learn how to turn off Dark Mode, please see: Use Dark Mode on your iPhone and iPad - Apple Support

Hello annelize288!

Please provide a screenshot of what your keyboard looks like, in order to help us better understand this issue.

Looking forward to your reply!

Most Apple devices have spacebars and you have not told us enough to help.

You’re welcome! 😊