It’s a little hard to comprehend without any further context.
Percentage of what exactly?
A pitch instrument could be marked with anything really, apples for up and oranges for down.
Being called an “attitude indicator” or “artificial horizon” it would mean show the difference between level flight and higher or lower pitch attitudes.
Considering everything else which is measured or indicated in degrees: flight control defection, roll rates and pitch rates.
It would be most logical to have a degree scale.
I have flown with angle of attack indicators that were color coded.
You also need to consider international design standards and certification requirements.
Doesnt answer your question I guess.