"<"span style="color:blue">some text" does not work
Changing text colour does not work if Sanitization is set to "Only allow secure html tags" or "Allow styles". You need to set it to "Allow dangerous html tags".
Don't know what is dangerous in this, but it is the only way I have succeed to change text colour.

Jim
@jimtremblay Thanks for the answer!
@js418 Now, you can allow it!
Most helpful comment
Changing text colour does not work if Sanitization is set to "Only allow secure html tags" or "Allow styles". You need to set it to "Allow dangerous html tags".
Don't know what is dangerous in this, but it is the only way I have succeed to change text colour.
Jim