docs: mention truecolor

README.md

@@ -1322,12 +1322,19 @@ terminals. Many terminals also support customization of these colors through col
 
 Type `source ~/.p10k.zsh` to apply your changes to the current Zsh session.
 
-To see how different colors look in your terminal, run the following command:
+To see how different numbered colors look in your terminal, run the following command:
 
 ```zsh
 for i in {0..255}; do print -Pn "%K{$i}  %k%F{$i}${(l:3::0:)i}%f " ${${(M)$((i%6)):#3}:+$'\n'}; done
 ```
 
+If your terminal supports truecolor, you can use 24-bit colors in the `#RRGGBB` format in addition
+to the numbered colors.
+
+```zsh
+typeset -g POWERLEVEL9K_TIME_FOREGROUND='#FF0000'
+```
+
 *Related:*
   - [Directory is difficult to see in prompt when using Rainbow style.](
       #directory-is-difficult-to-see-in-prompt-when-using-rainbow-style)