I bought a lower-end smartphone as a replacement. I can't locate the selection in Settings for changing my colors. There is no Tools selection. Not earth-shattering, but still...thanks.
You don't say what phone you have, but font changes might be found near something like:
settings > display > font type and size
Background colors are usually an app issue. Many apps do not let you change this.
Some apps let you choose between light and dark backgrounds (day vs night mode).