Setting hidden of lines very slow

[Jim Lambert via use-livecode]

So I am looking to hide any line that contains no textcolor anywhere.

You might save into a variable the HTMLTEXT of all the lines that contain the textcolor.
Also save the HTMLTEXT of the whole field into another variable.
Then in a blink of an eye you can instantly switch between the entire text and just the lines with colored characters - and back again.

Jim Lambert