A family of Microsoft relational database management systems designed for ease of use.
Hi again,
Many moons ago I read something about a maximum of individual cells that can be formatted. You could try the following: insert the column "Marked". Instead of now changing the formatting for individual cells/tasks, for those set Marked to Yes then in Text Styles (on the Format ribbon) set a background for "Marked Taks". That may seriously limit the number of individual cells coloured and should solve your problem.
And BTW, formatting is saved with the View so when you cahnge views you may no longer see the formatting.
Greetings,