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The 'Halftone' setting controls how bright or faint the existing linework displays when you go into 'Sketch' mode in REVIT. You can find the 'Halftone' setting under the 'Manage' tab on the ribbon.
I definitely do recall being annoyed in the past when you go into sketch mode and you have the pink / magenta lines and the rest of the model all but disappears.
I believe it may also depend on your monitor, resolution, video card and display settings. By default it usually works ok so this is why most people never come across the problem.
But when you do . . . . . . it sure is annoying.