Hi Hamed8080,
Thanks for contacting Apple Support Communities!
We understand that you're sharing a Note via iCloud and some participants are unable to see the note in Dark Mode.
Dark Mode is dependent on the operating system itself. If the participants are using a web browser which supports Dark Mode, they can also view the note in Dark Mode.
This resource explains how Dark Mode works on Mac for example: How to use Dark Mode on your Mac - Apple Support
How Dark Mode works with some apps and features
Some apps and features have special Dark Mode settings or behaviors.
Mail. To use a light background for email messages while Dark Mode is turned on, open Mail and choose Mail > Preferences, then click the Viewing tab and deselect “Use dark backgrounds for messages.”
Maps. To use a light background for maps while Dark Mode is turned on, open Maps and choose Maps > Preferences, then select ”Always use light map appearance.” In earlier versions of macOS, click View in the menu bar in Maps, then deselect Use Dark Map.
Notes. To use a light background for notes while Dark Mode is turned on, open Notes and choose Notes > Preferences, then deselect “Use dark backgrounds for note content.”
Safari. When you use Dark Mode, Safari automatically shows a website in Dark Mode if the website has been designed to support it. If the website doesn't support Dark Mode, you can use Safari Reader to read articles in Dark Mode.
TextEdit. To use a light background for documents while Dark Mode is turned on, click View in the menu bar in TextEdit, then deselect Use Dark Background for Windows. (Requires macOS Mojave 10.14.2 or later.)
Dynamic Desktop. If you turn on Dark Mode while using Dynamic Desktop, the desktop may change to the dark still image. You can change this setting in Desktop & Screen Saver preferences.
Which device are you using when you notice the color changes in your Note? Is the color changing in the same note or does this happen when you create a new note and paste the colored text into the new note? This will help us to isolate this behavior further.
Cheers!
